pkt_sched: Add qdisc->ops->peek() implementation.

Add qdisc->ops->peek() implementation for work-conserving qdiscs.
With feedback from Patrick McHardy.

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index a119599..2898d9d 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -541,6 +541,7 @@
 	.priv_size	=	sizeof(struct fifo_sched_data),
 	.enqueue	=	tfifo_enqueue,
 	.dequeue	=	qdisc_dequeue_head,
+	.peek		=	qdisc_peek_head,
 	.requeue	=	qdisc_requeue,
 	.drop		=	qdisc_queue_drop,
 	.init		=	tfifo_init,