Increase session pool size on Darwin so we don't run out of sessions.

[bzbarsky-apple]

We want to have enough sessions for all the subscriptions we will want
to have.

Problem

Default pool size is too small for the number of devices we might want simultaneous subscriptions to.

Change overview

Bump the size.

[github-actions]

PR #20086: Size comparison from d4bb6ee to 2b68cf8

Increases (5 builds for cc13x2_26x2, cyw30739, nrfconnect, telink)

platform	target	config	section	d4bb6ee	2b68cf8	change	% change
cc13x2_26x2	lock-ftd	LP_CC2652R7	(read only)	667311	667319	8	0.0
			.text	590848	590856	8	0.0
cyw30739	lock	cyw930739m2evb_01	(read/write)	581966	581974	8	0.0
			.app_xip_area	458776	458784	8	0.0
	ota-requestor-no-progress-logging	cyw930739m2evb_01	(read/write)	583186	583194	8	0.0
			.app_xip_area	461036	461044	8	0.0
nrfconnect	all-clusters-minimal-app	nrf52840dk_nrf52840	(read/write)	1155139	1155155	16	0.0
			text	799264	799268	4	0.0
telink	light-switch-app	tlsr9518adk80d	text	564538	564542	4	0.0

Decreases (2 builds for cc13x2_26x2, telink)

platform	target	config	section	d4bb6ee	2b68cf8	change	% change
cc13x2_26x2	lock-ftd	LP_CC2652R7	(read/write)	175824	175816	-8	-0.0
telink	lighting-app	tlsr9518adk80d	text	580900	580898	-2	-0.0

Full report (30 builds for cc13x2_26x2, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, p6, telink)

platform	target	config	section	d4bb6ee	2b68cf8	change	% change
cc13x2_26x2	all-clusters-app	LP_CC2652R7	(read only)	664779	664779	0	0.0
			(read/write)	188212	188212	0	0.0
			.bss	75884	75884	0	0.0
			.data	3356	3356	0	0.0
			.rodata	87891	87891	0	0.0
			.text	576572	576572	0	0.0
	all-clusters-minimal-app	LP_CC2652R7	(read only)	653511	653511	0	0.0
			(read/write)	198776	198776	0	0.0
			.bss	75180	75180	0	0.0
			.data	3356	3356	0	0.0
			.rodata	91359	91359	0	0.0
			.text	561836	561836	0	0.0
	lock-ftd	LP_CC2652R7	(read only)	667311	667319	8	0.0
			(read/write)	175824	175816	-8	-0.0
			.bss	72916	72916	0	0.0
			.data	3280	3280	0	0.0
			.rodata	75983	75983	0	0.0
			.text	590848	590856	8	0.0
	lock-mtd	LP_CC2652R7	(read only)	616727	616727	0	0.0
			(read/write)	146032	146032	0	0.0
			.bss	68636	68636	0	0.0
			.data	3280	3280	0	0.0
			.rodata	75863	75863	0	0.0
			.text	540376	540376	0	0.0
	pump-app	LP_CC2652R7	(read only)	676759	676759	0	0.0
			(read/write)	167232	167232	0	0.0
			.bss	73004	73004	0	0.0
			.data	3280	3280	0	0.0
			.rodata	88215	88215	0	0.0
			.text	588060	588060	0	0.0
	pump-controller-app	LP_CC2652R7	(read only)	662611	662611	0	0.0
			(read/write)	181500	181500	0	0.0
			.bss	73124	73124	0	0.0
			.data	3276	3276	0	0.0
			.rodata	84067	84067	0	0.0
			.text	578064	578064	0	0.0
	shell	LP_CC2652R7	(read only)	657250	657250	0	0.0
			(read/write)	191244	191244	0	0.0
			.bss	78188	78188	0	0.0
			.data	3360	3360	0	0.0
			.rodata	84650	84650	0	0.0
			.text	572284	572284	0	0.0
cyw30739	light	cyw930739m2evb_01	(read/write)	580398	580398	0	0.0
			.app_xip_area	457400	457400	0	0.0
			.bss	65960	65960	0	0.0
			.data	716	716	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
	lock	cyw930739m2evb_01	(read/write)	581966	581974	8	0.0
			.app_xip_area	458776	458784	8	0.0
			.bss	66152	66152	0	0.0
			.data	720	720	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
	ota-requestor-no-progress-logging	cyw930739m2evb_01	(read/write)	583186	583194	8	0.0
			.app_xip_area	461036	461044	8	0.0
			.bss	65168	65168	0	0.0
			.data	660	660	0	0.0
			.rodata	0	0	0	0.0
			.text	112	112	0	0.0
efr32	lighting-app	BRD4161A	(read/write)	1081116	1081116	0	0.0
			.bss	134764	134764	0	0.0
			.data	2048	2048	0	0.0
			.text	944284	944284	0	0.0
		BRD4161A+rpc	(read/write)	1135412	1135412	0	0.0
			.bss	151452	151452	0	0.0
			.data	2260	2260	0	0.0
			.text	981680	981680	0	0.0
		BRD4161A+rs911x	(read/write)	943648	943648	0	0.0
			.bss	140480	140480	0	0.0
			.data	2048	2048	0	0.0
			.text	801100	801100	0	0.0
	lock-app	BRD4161A+wf200	(read/write)	1120920	1120920	0	0.0
			.bss	140912	140912	0	0.0
			.data	2060	2060	0	0.0
			.text	977928	977928	0	0.0
	window-app	BRD4161A	(read/write)	1066396	1066396	0	0.0
			.bss	134844	134844	0	0.0
			.data	2076	2076	0	0.0
			.text	929452	929452	0	0.0
esp32	all-clusters-app	c3devkit	(read only)	1018282	1018282	0	0.0
			(read/write)	1486482	1486482	0	0.0
			.dram0.bss	71856	71856	0	0.0
			.dram0.data	14624	14624	0	0.0
			.flash.rodata	214576	214576	0	0.0
			.flash.text	1018282	1018282	0	0.0
			.iram0.text	62902	62902	0	0.0
		m5stack	(read only)	1072455	1072455	0	0.0
			(read/write)	488576	488576	0	0.0
			.dram0.bss	77376	77376	0	0.0
			.dram0.data	34144	34144	0	0.0
			.flash.rodata	245060	245060	0	0.0
			.flash.text	1067071	1067071	0	0.0
			.iram0.text	123267	123267	0	0.0
k32w	light	k32w061+release	(read/write)	659568	659568	0	0.0
			.bss	71284	71284	0	0.0
			.data	1992	1992	0	0.0
			.text	580492	580492	0	0.0
	lock	k32w061+release	(read/write)	685824	685824	0	0.0
			.bss	71756	71756	0	0.0
			.data	2004	2004	0	0.0
			.text	606264	606264	0	0.0
linux	chip-tool-no-interactive-ipv6only	arm64	(read only)	9905332	9905332	0	0.0
			(read/write)	675649	675649	0	0.0
			.bss	42609	42609	0	0.0
			.data	1152	1152	0	0.0
			.data.rel.ro	614640	614640	0	0.0
			.dynamic	528	528	0	0.0
			.got	13440	13440	0	0.0
			.init	24	24	0	0.0
			.init_array	192	192	0	0.0
			.rodata	472196	472196	0	0.0
			.text	7893540	7893540	0	0.0
	thermostat-no-ble	arm64	(read only)	2591020	2591020	0	0.0
			(read/write)	158897	158897	0	0.0
			.bss	65841	65841	0	0.0
			.data	1704	1704	0	0.0
			.data.rel.ro	83256	83256	0	0.0
			.dynamic	528	528	0	0.0
			.got	5072	5072	0	0.0
			.init	24	24	0	0.0
			.init_array	400	400	0	0.0
			.rodata	165004	165004	0	0.0
			.text	2186288	2186288	0	0.0
mbed	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2446560	2446560	0	0.0
			.bss	215708	215708	0	0.0
			.data	5872	5872	0	0.0
			.text	1409204	1409204	0	0.0
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	(read/write)	1174287	1174287	0	0.0
			bss	144658	144658	0	0.0
			rodata	141136	141136	0	0.0
			text	809564	809564	0	0.0
	all-clusters-minimal-app	nrf52840dk_nrf52840	(read/write)	1155139	1155155	16	0.0
			bss	143894	143894	0	0.0
			rodata	133068	133068	0	0.0
			text	799264	799268	4	0.0
p6	all-clusters-app	default	(read/write)	2562440	2562440	0	0.0
			.bss	150888	150888	0	0.0
			.data	2776	2776	0	0.0
			.text	1520704	1520704	0	0.0
	all-clusters-minimal-app	default	(read/write)	2508288	2508288	0	0.0
			.bss	150168	150168	0	0.0
			.data	2776	2776	0	0.0
			.text	1466552	1466552	0	0.0
	light-app	default	(read/write)	2438440	2438440	0	0.0
			.bss	142224	142224	0	0.0
			.data	2592	2592	0	0.0
			.text	1396704	1396704	0	0.0
	lock-app	default	(read/write)	2464704	2464704	0	0.0
			.bss	142072	142072	0	0.0
			.data	2600	2600	0	0.0
			.text	1422968	1422968	0	0.0
telink	light-switch-app	tlsr9518adk80d	(read/write)	797580	797580	0	0.0
			bss	72336	72336	0	0.0
			noinit	40416	40416	0	0.0
			text	564538	564542	4	0.0
	lighting-app	tlsr9518adk80d	(read/write)	817440	817440	0	0.0
			bss	73172	73172	0	0.0
			noinit	40416	40416	0	0.0
			text	580900	580898	-2	-0.0