mgcp_test: add returncode check

The returncode of get_conn_id_from_response() is unchecked, which
is intentional since some of the test messages will intentionally cause
this function to fail (the response does not inclde a connection
identifier). This means it makes no sense to assert this function
to a fixed value.

In order to spot regressions better print a log message depending
on the return code.

Change-Id: I9bce9ca39b7751b557374b7ab57c6c9005bcdb7d
Fixes: Coverity CID#180534
diff --git a/tests/mgcp/mgcp_test.c b/tests/mgcp/mgcp_test.c
index 1c57347..ee49eef 100644
--- a/tests/mgcp/mgcp_test.c
+++ b/tests/mgcp/mgcp_test.c
@@ -636,6 +636,7 @@
 	int i;
 	struct mgcp_conn_rtp *conn = NULL;
 	char last_conn_id[256];
+	int rc;
 
 	cfg = mgcp_config_alloc();
 
@@ -675,9 +676,14 @@
 			OSMO_ASSERT(false);
 		}
 
-		if (msg)
-			get_conn_id_from_response(msg->data, last_conn_id,
-						  sizeof(last_conn_id));
+		if (msg) {
+			rc = get_conn_id_from_response(msg->data, last_conn_id,
+						       sizeof(last_conn_id));
+			if (rc)
+				printf("(response contains a connection id)\n");
+			else
+				printf("(response does not contain a connection id)\n");
+		}
 
 		msgb_free(msg);