net: sched: avoid costly atomic operation in fq_dequeue()

Standard qdisc API to setup a timer implies an atomic operation on every
packet dequeue : qdisc_unthrottled()

It turns out this is not really needed for FQ, as FQ has no concept of
global qdisc throttling, being a qdisc handling many different flows,
some of them can be throttled, while others are not.

Fix is straightforward : add a 'bool throttle' to
qdisc_watchdog_schedule_ns(), and remove calls to qdisc_unthrottled()
in sch_fq.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_tbf.c

@@ -268,7 +268,8 @@ static struct sk_buff *tbf_dequeue(struct Qdisc *sch)
 		}
 
 		qdisc_watchdog_schedule_ns(&q->watchdog,
-					   now + max_t(long, -toks, -ptoks));
+					   now + max_t(long, -toks, -ptoks),
+					   true);
 
 		/* Maybe we have a shorter packet in the queue,
 		   which can be sent now. It sounds cool,