net_sched: keep backlog updated with qlen

For gso_skb we only update qlen, backlog should be updated too.

Note, it is correct to just update these stats at one layer,
because the gso_skb is cached there.

Reported-by: Stas Nichiporovich <stasn77@gmail.com>
Fixes: 2ccccf5f ("net_sched: update hierarchical backlog too")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>