add a more descriptive error message on no (or no usable) candidates

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@4171 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/mod/endpoints/mod_dingaling/mod_dingaling.c

@@ -703,6 +703,7 @@ static int activate_rtp(struct private_object *tech_pvt)
 	}
 
     if (!(tech_pvt->remote_ip && tech_pvt->remote_port)) {
+		switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "No valid candidates received!\n");
         return 0;
     }