etf: Cancel timer if there are no pending skbs

There is no point in firing the qdisc watchdog if there are no future
skbs pending in the queue and the watchdog had been set previously.

Signed-off-by: Jesus Sanchez-Palencia <jesus.s.palencia@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_etf.c

@@ -117,8 +117,10 @@ static void reset_watchdog(struct Qdisc *sch)
 	struct sk_buff *skb = etf_peek_timesortedlist(sch);
 	ktime_t next;
 
-	if (!skb)
+	if (!skb) {
+		qdisc_watchdog_cancel(&q->watchdog);
 		return;
+	}
 
 	next = ktime_sub_ns(skb->tstamp, q->delta);
 	qdisc_watchdog_schedule_ns(&q->watchdog, ktime_to_ns(next));