sch_netem: more precise length of packets

With TSO/GSO/GRO packets, skb->len doesn't represent
a precise amount of bytes on wire.
This patch replace skb->len with qdisc_pkt_len(skb)
which is more precise.
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Acked-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_netem.c

@@ -495,7 +495,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 				now = netem_skb_cb(last)->time_to_send;
 			}
 
-			delay += packet_len_2_sched_time(skb->len, q);
+			delay += packet_len_2_sched_time(qdisc_pkt_len(skb), q);
 		}
 
 		cb->time_to_send = now + delay;