tests: Bluetooth: Mesh: Increase subnet bridge ivu test time

Commit increases IV index update testing time for subnet
bridge.

Due to change in startup time for external crystal, test
time expires earlier than test scenario reaches end.

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

tests/bsim/bluetooth/mesh/src/test_brg.c

@@ -18,7 +18,7 @@
 LOG_MODULE_REGISTER(test_brg, LOG_LEVEL_INF);
 
 #define WAIT_TIME          32  /*seconds*/
-#define WAIT_TIME_IVU_TEST 240 /* seconds */
+#define WAIT_TIME_IVU_TEST 250 /* seconds */
 #define BEACON_INTERVAL    10  /*seconds */
 
 #define PROV_ADDR         0x0001