drv/bluetooth_btstack: don't advertise after disconnect

BTStack has a "feature" where advertising is started automatically [1].

To be consistent with other hubs, we don't want this to happen.

Fixes: pybricks/support#849

[1]: https://github.com/bluekitchen/btstack/blob/ffc05fad031013a636a5d1085532b4ecb83a70a3/src/hci.c#L2789

CHANGELOG.md

@@ -4,6 +4,12 @@
 
 ## [Unreleased]
 
+### Fixed
+- Fixed SPIKE/MINDSTORMS hubs advertising after disconnect while user program
+  is still running ([support#849]).
+
+[support#849]: https://github.com/pybricks/support/issues/849
+
 ## [3.2.0c1] - 2022-12-09
 
 ### Fixed

lib/pbio/drv/bluetooth/bluetooth_btstack.c

@@ -265,6 +265,9 @@ static void packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packe
             // HCI_ROLE_MASTER means the connecting device is the peripheral and the hub is the central.
             if (hci_subevent_le_connection_complete_get_role(packet) == HCI_ROLE_SLAVE) {
                 le_con_handle = hci_subevent_le_connection_complete_get_connection_handle(packet);
+
+                // don't start advertising again on disconnect
+                gap_advertisements_enable(false);
             } else {
                 // If we aren't waiting for a handset connection, this must be a different connection.
                 if (handset.con_state != CON_STATE_WAIT_CONNECT) {