[FRR]zebra: Fix fpm multipath encap addition (sonic-net#17247)

Why I did it
To fix the EVPN type5 failure seen in FRR when there are multipaths for nexthop. The type5 routes were queued

show ip route vrf Vrf1
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
       f - OpenFabric,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

VRF Vrf1:
B>q 5.5.5.0/24 [200/0] via 30.0.0.2, Vlan100 onlink, weight 1, 00:00:40
  q                    via 40.0.0.3, Vlan100 onlink, weight 1, 00:00:40
C>* 10.0.0.0/24 is directly connected, Vlan10, 00:00:43
B>q 100.0.0.0/24 [200/0] via 30.0.0.2, Vlan100 onlink, weight 1, 00:00:40
  q                      via 40.0.0.3, Vlan100 onlink, weight 1, 00:00:40
Work item tracking
Microsoft ADO (number only):
How I did it
Porting the FRR fix FRRouting/frr#14835

How to verify it
Validated EVPN multipath with the scenario and confirmed its working.

src/sonic-frr/patch/0032-zebra-Fix-fpm-multipath-encap-addition.patch

@@ -0,0 +1,58 @@
+From b7ac2397103fe7d347d0766bd9966ff2302403c5 Mon Sep 17 00:00:00 2001
+From: dgsudharsan <[email protected]>
+Date: Tue, 21 Nov 2023 01:17:24 +0000
+Subject: [PATCH] zebra: Fix fpm multipath encap addition The fpm code path in
+ building a ecmp route for evpn has a bug that caused it to not add the encap
+ attribute to the netlink message.  See
+ #f0f7b285b99dbd971400d33feea007232c0bd4a9 for the single path case being
+ fixed.
+
+
+diff --git a/zebra/rt_netlink.c b/zebra/rt_netlink.c
+index 71505e037a..6bdc15592c 100644
+--- a/zebra/rt_netlink.c
++++ b/zebra/rt_netlink.c
+@@ -2330,6 +2330,16 @@ ssize_t netlink_route_multipath_msg_encode(int cmd,
+ 					    tag))
+ 					return 0;
+
++				/*
++				 * Add encapsulation information when installing via
++				 * FPM.
++				 */
++				if (fpm) {
++					if (!netlink_route_nexthop_encap(
++						    &req->n, datalen, nexthop))
++						return 0;
++				}
++
+ 				if (!setsrc && src1) {
+ 					if (p->family == AF_INET)
+ 						src.ipv4 = src1->ipv4;
+@@ -2343,23 +2353,6 @@ ssize_t netlink_route_multipath_msg_encode(int cmd,
+
+ 		nl_attr_nest_end(&req->n, nest);
+
+-		/*
+-		 * Add encapsulation information when installing via
+-		 * FPM.
+-		 */
+-		if (fpm) {
+-			for (ALL_NEXTHOPS_PTR(dplane_ctx_get_ng(ctx),
+-					      nexthop)) {
+-				if (CHECK_FLAG(nexthop->flags,
+-					       NEXTHOP_FLAG_RECURSIVE))
+-					continue;
+-				if (!netlink_route_nexthop_encap(
+-					    &req->n, datalen, nexthop))
+-					return 0;
+-			}
+-		}
+-
+-
+ 		if (setsrc) {
+ 			if (p->family == AF_INET) {
+ 				if (!nl_attr_put(&req->n, datalen, RTA_PREFSRC,
+-- 
+2.17.1
+

src/sonic-frr/patch/series

@@ -31,3 +31,4 @@ cross-compile-changes.patch
 0029-bgpd-Handle-MP_REACH_NLRI-malformed-packets-with-ses.patch
 0030-bgpd-Treat-EOR-as-withdrawn-to-avoid-unwanted-handli.patch
 0031-bgpd-Ignore-handling-NLRIs-if-we-received-MP_UNREACH.patch
+0032-zebra-Fix-fpm-multipath-encap-addition.patch