net: sched: Add the invalid handle check in qdisc_class_find

Add the invalid handle "0" check to avoid unnecessary search, because
the qdisc uses the skb->priority as the handle value to look up, and
it is "0" usually.

Signed-off-by: Gao Feng <gfree.wind@vip.163.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sch_generic.h

@@ -393,6 +393,9 @@ qdisc_class_find(const struct Qdisc_class_hash *hash, u32 id)
 	struct Qdisc_class_common *cl;
 	unsigned int h;
 
+	if (!id)
+		return NULL;
+
 	h = qdisc_class_hash(id, hash->hashmask);
 	hlist_for_each_entry(cl, &hash->hash[h], hnode) {
 		if (cl->classid == id)