pkt_sched: Fix sch_sfq vs tcf_bind_filter oops

Since there was added ->tcf_chain() method without ->bind_tcf() to
sch_sfq class options, there is oops when a filter is added with
the classid parameter.

Fixes commit 7d2681a6
netdev thread: null pointer at cls_api.c

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Reported-by: Franchoze Eric <franchoze@yandex.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>