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 7d2681a6ff4f9ab5e48d02550b4c6338f1638998
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>

net/sched/sch_sfq.c

@@ -513,6 +513,12 @@ static unsigned long sfq_get(struct Qdisc *sch, u32 classid)
 	return 0;
 }
 
+static unsigned long sfq_bind(struct Qdisc *sch, unsigned long parent,
+			      u32 classid)
+{
+	return 0;
+}
+
 static struct tcf_proto **sfq_find_tcf(struct Qdisc *sch, unsigned long cl)
 {
 	struct sfq_sched_data *q = qdisc_priv(sch);
@@ -567,6 +573,7 @@ static void sfq_walk(struct Qdisc *sch, struct qdisc_walker *arg)
 static const struct Qdisc_class_ops sfq_class_ops = {
 	.get		=	sfq_get,
 	.tcf_chain	=	sfq_find_tcf,
+	.bind_tcf	=	sfq_bind,
 	.dump		=	sfq_dump_class,
 	.dump_stats	=	sfq_dump_class_stats,
 	.walk		=	sfq_walk,