bsc: Permit MGCP messages from random ports on BSC side

Change-Id: Ie8896edc3f4310a78b584fd4ad017b77bda22afb

bsc/BSC_Tests.ttcn

@@ -191,7 +191,7 @@ function f_init_mgcp(charstring id) runs on test_CT {
 	};
 	var MGCP_conn_parameters mgcp_pars := {
 		callagent_ip := mp_bsc_ip,
-		callagent_udp_port := 2727,
+		callagent_udp_port := -1,
 		mgw_ip := mp_test_ip,
 		mgw_udp_port := 2427
 	};