Raise 'connecting' flag for UDP requests as well.

This is because the query should be sent as soon as the socket is
writable as well.

refs #65

src/knot/server/xfr-handler.c

@@ -271,10 +271,11 @@ static int xfr_task_connect(knot_ns_xfr_t *rq)
 			socket_close(fd);
 			return KNOT_ECONNREFUSED;
 		}
-
-		rq->flags |= XFR_FLAG_CONNECTING;
 	}
 
+	/* Set up for UDP as well to trigger 'send query' event. */
+	rq->flags |= XFR_FLAG_CONNECTING;
+
 	/* Store new socket descriptor. */
 	rq->session = fd;
 	return KNOT_EOK;