net_sched: get rid of unnecessary dev_qdisc_reset()

Resetting old qdisc on dev_queue->qdisc_sleeping in
dev_qdisc_reset() is redundant, because this qdisc,
even if not same with dev_queue->qdisc, is reset via
qdisc_put() right after calling dev_graft_qdisc() when
hitting refcnt 0.

This is very easy to observe with qdisc_reset() tracepoint
and stack traces.

Reported-by: Václav Zindulka <vaclav.zindulka@tlapnet.cz>
Tested-by: Václav Zindulka <vaclav.zindulka@tlapnet.cz>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>