mgcp_network.c: Address compiler warning on return

When adding the "omit RTCP" the method started to return with
a proper return statement.

mgcp_network.c: In function ‘send_to’:
mgcp_network.c:233:1: warning: control reaches end of non-void function [-Wreturn-type]

openbsc/src/libmgcp/mgcp_network.c

@@ -230,6 +230,8 @@ static int send_to(struct mgcp_endpoint *endp, int dest, int is_rtp,
 					endp->bts_end.rtcp_port, buf, rc);
 		}
 	}
+
+	return 0;
 }
 
 static int receive_from(struct mgcp_endpoint *endp, int fd, struct sockaddr_in *addr,