mgcp: Indicate where the sending failed

The log message does not help and says where the data is
being sent to. This is because we have both a RTP and RTCP
port. Remember if we failed with RTCP or RTP and improve
the log message.

I was searching a case where the port was bound to a local
address (e.g. 127.0.0.1) and tried to send the data to a
public one (e.g. 8.8.8.8).
diff --git a/openbsc/src/libmgcp/mgcp_network.c b/openbsc/src/libmgcp/mgcp_network.c
index c39b627..abce6e4 100644
--- a/openbsc/src/libmgcp/mgcp_network.c
+++ b/openbsc/src/libmgcp/mgcp_network.c
@@ -94,6 +94,7 @@
 {
 	static char buf[] = { MGCP_DUMMY_LOAD };
 	int rc;
+	int was_rtcp = 0;
 
 	rc = mgcp_udp_send(endp->net_end.rtp.fd, &endp->net_end.addr,
 			   endp->net_end.rtp_port, buf, 1);
@@ -104,6 +105,7 @@
 	if (endp->tcfg->omit_rtcp)
 		return rc;
 
+	was_rtcp = 1;
 	rc = mgcp_udp_send(endp->net_end.rtcp.fd, &endp->net_end.addr,
 			   endp->net_end.rtcp_port, buf, 1);
 
@@ -112,8 +114,10 @@
 
 failed:
 	LOGP(DMGCP, LOGL_ERROR,
-	     "Failed to send dummy packet: %s on: 0x%x to %s\n",
-	     strerror(errno), ENDPOINT_NUMBER(endp), inet_ntoa(endp->net_end.addr));
+		"Failed to send dummy %s packet: %s on: 0x%x to %s:%d\n",
+		was_rtcp ? "RTCP" : "RTP",
+		strerror(errno), ENDPOINT_NUMBER(endp), inet_ntoa(endp->net_end.addr),
+		was_rtcp ? endp->net_end.rtcp_port : endp->net_end.rtp_port);
 
 	return -1;
 }