net: mqtt-sn: Update MQTT-SN Unit Tests

Fixes: #78010
This commit adds tests for the "Gateway Advertisement and Discovery"
process. This includes tests for handling SEARCHGW, GWINFO, and ADVERTISE
as well as manually adding a Gateway for use. Gateway pruning when
missing ADVERTISE messages is also tested.

Signed-off-by: Kenneth Witham <[email protected]>

Author: SpontaneousDuck

tests/net/lib/mqtt_sn_client/prj.conf

@@ -18,3 +18,8 @@ CONFIG_ZTEST_STACK_SIZE=8192
 CONFIG_STACK_USAGE=y
 CONFIG_STACK_SENTINEL=y
 CONFIG_DEBUG=y
+
+# Reduce MQTT_SN delay times for testing
+CONFIG_MQTT_SN_LIB_T_SEARCHGW=0
+CONFIG_MQTT_SN_LIB_T_GWINFO=0
+CONFIG_MQTT_SN_LIB_N_ADV=1