We need to update backlog too when we update qlen.

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