sch_hfsc: always keep backlog updated

sch_hfsc: always keep backlog updated

hfsc updates backlog lazily, that is only when we
dump the stats. This is problematic after we begin to
update backlog in qdisc_tree_reduce_backlog().

Reported-by: Stas Nichiporovich <stasn77@gmail.com>
Tested-by: Stas Nichiporovich <stasn77@gmail.com>
Fixes: 329ca48484a3 ("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>