[load_balancer] fix chaining and freeing of probing packs

Some probing packs may be freed before ending circulating the list (if the prob sending fails), so we need to take care of the linking.

modules/load_balancer/lb_prober.c

@@ -102,6 +102,7 @@ void lb_do_probing(struct lb_data *data)
 		pack->uri.s = (char*)(pack+1);
 		memcpy(pack->uri.s, dst->uri.s, dst->uri.len);
 		pack->uri.len = dst->uri.len;
+		pack->next = NULL;
 
 		pack->params.id = dst->id;
 
@@ -117,7 +118,9 @@ void lb_do_probing(struct lb_data *data)
 	lock_stop_read( ref_lock );
 
 	/* now send all the probs, outside the lock */
-	for( pack = pack_head ; pack ; pack=pack->next ) {
+	for( pack = pack_head ; pack ; pack=pack_last ) {
+
+		pack_last = pack->next;
 
 		if (lb_tmb.t_request( &lb_probe_method, &pack->uri, &pack->uri,
 		&lb_probe_from, NULL, NULL, NULL, lb_probing_callback,