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_dsmark.c b/net/sched/sch_dsmark.c
index ba43aab..3e49147 100644
--- a/net/sched/sch_dsmark.c
+++ b/net/sched/sch_dsmark.c
@@ -313,6 +313,15 @@
 	return skb;
 }
 
+static struct sk_buff *dsmark_peek(struct Qdisc *sch)
+{
+	struct dsmark_qdisc_data *p = qdisc_priv(sch);
+
+	pr_debug("dsmark_peek(sch %p,[qdisc %p])\n", sch, p);
+
+	return p->q->ops->peek(p->q);
+}
+
 static int dsmark_requeue(struct sk_buff *skb, struct Qdisc *sch)
 {
 	struct dsmark_qdisc_data *p = qdisc_priv(sch);
@@ -496,6 +505,7 @@
 	.priv_size	=	sizeof(struct dsmark_qdisc_data),
 	.enqueue	=	dsmark_enqueue,
 	.dequeue	=	dsmark_dequeue,
+	.peek		=	dsmark_peek,
 	.requeue	=	dsmark_requeue,
 	.drop		=	dsmark_drop,
 	.init		=	dsmark_init,