Merge branch 'sch-accurate-backlog'

Cong Wang says:

====================
net_sched: update backlog for hierarchical qdisc's

For hierarchical qdisc like HTB, we currently only update its qlen
but leave its backlog as zero:

    qdisc htb 1: dev eth0 root refcnt 2 r2q 10 default 1 direct_packets_stat 0 ver 3.17
     Sent 172680457356 bytes 222469449 pkt (dropped 0, overlimits 123575834 requeues 0)
     backlog 0b 72p requeues 0

This patchset makes backlog as accurate as qlen.

v3: rebase and fix the n==0 case for qdisc_tree_reduce_backlog()
v2: rebase and update changelog, not code change
====================

Signed-off-by: David S. Miller <davem@davemloft.net>