sch_htb: make htb_qlen_notify() idempotent

htb_qlen_notify() always deactivates the HTB class and in fact could
trigger a warning if it is already deactivated. Therefore, it is not
idempotent and not friendly to its callers, like fq_codel_dequeue().

Let's make it idempotent to ease qdisc_tree_reduce_backlog() callers'
life.

Reported-by: Gerrard Tai <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Acked-by: Jamal Hadi Salim <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>

Author: congwang

net/sched/sch_htb.c

@@ -1485,6 +1485,8 @@ static void htb_qlen_notify(struct Qdisc *sch, unsigned long arg)
 {
 	struct htb_class *cl = (struct htb_class *)arg;
 
+	if (!cl->prio_activity)
+		return;
 	htb_deactivate(qdisc_priv(sch), cl);
 }