director: Fix updating director connection's last_output timestamp

It was previously updated only in ostream's flush callback, which was called
only when there were a lot of output. This only caused the "last output"
timestamp in disconnection log lines to be wrong.

src/director/director-connection.c

@@ -2299,6 +2299,7 @@ void director_connection_send(struct director_connection *conn,
 			timeout_add_short(0, director_disconnect_write_error, conn);
 	} else {
 		conn->dir->ring_traffic_output += len;
+		conn->last_output = ioloop_timeval;
 	}
 }