client: use string as connection identifier

The test that tests the cancelation of a pending mgcp message
uses an integer as connection identifier, which leads to a
segfault since connection identifiers are represented as strings.

Use a string as connection identifier.

Change-Id: I395a23c1828cf216031d69d481ad35dd458ee7d4
diff --git a/tests/mgcp_client/mgcp_client_test.c b/tests/mgcp_client/mgcp_client_test.c
index 172faac..ef2fca8 100644
--- a/tests/mgcp_client/mgcp_client_test.c
+++ b/tests/mgcp_client/mgcp_client_test.c
@@ -236,7 +236,7 @@
 		.endpoint = "23@mgw",
 		.audio_port = 1234,
 		.call_id = 47,
-		.conn_id = 11,
+		.conn_id = "11",
 		.conn_mode = MGCP_CONN_RECV_SEND,
 		.presence = (MGCP_MSG_PRESENCE_ENDPOINT | MGCP_MSG_PRESENCE_CALL_ID
 			     | MGCP_MSG_PRESENCE_CONN_ID | MGCP_MSG_PRESENCE_CONN_MODE),