MGCP_Test: add testcase TC_one_crcx_loopback_rtp_ipv6

There is an TC_one_crcx_loopback_rtp, an ipv6 variant can be added with
minimal effort.

Change-Id: If16ee5186fa697caa9cc404b7159be054cac5196
diff --git a/mgw/MGCP_Test.ttcn b/mgw/MGCP_Test.ttcn
index 5575f7a..c1e263a 100644
--- a/mgw/MGCP_Test.ttcn
+++ b/mgw/MGCP_Test.ttcn
@@ -1727,6 +1727,9 @@
 	testcase TC_one_crcx_loopback_rtp() runs on dummy_CT {
 		 f_TC_one_crcx_loopback_rtp(mp_local_ipv4, mp_remote_ipv4, one_phase := true)
 	}
+	testcase TC_one_crcx_loopback_rtp_ipv6() runs on dummy_CT {
+		 f_TC_one_crcx_loopback_rtp(mp_local_ipv6, mp_remote_ipv6, one_phase := true)
+	}
 
 	/* Same as above, but we will intenionally not tell the MGW where to
 	 * send the outgoing traffic. The connection is still created in
@@ -2441,6 +2444,7 @@
 
 		execute(TC_one_crcx_receive_only_rtp());
 		execute(TC_one_crcx_loopback_rtp());
+		execute(TC_one_crcx_loopback_rtp_ipv6());
 		execute(TC_one_crcx_loopback_rtp_implicit());
 		execute(TC_two_crcx_and_rtp());
 		execute(TC_two_crcx_and_rtp_bidir());