workqueue: use cwq_set_max_active() helper for workqueue_set_max_active()

workqueue_set_max_active() may increase ->max_active without
activating delayed works and may make the activation order differ from
the queueing order.  Both aren't strictly bugs but the resulting
behavior could be a bit odd.

To make things more consistent, use cwq_set_max_active() helper which
immediately makes use of the newly increased max_mactive if there are
delayed work items and also keeps the activation order.

tj: Slight update to description.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -3413,7 +3413,7 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
 
 		if (!(wq->flags & WQ_FREEZABLE) ||
 		    !(gcwq->flags & GCWQ_FREEZING))
-			get_cwq(gcwq->cpu, wq)->max_active = max_active;
+			cwq_set_max_active(get_cwq(gcwq->cpu, wq), max_active);
 
 		spin_unlock_irq(&gcwq->lock);
 	}