net: sched: consistently use rcu_replace_pointer() in taprio_change()

According to Vinicius (and carefully looking through the whole
https://syzkaller.appspot.com/bug?extid=b65e0af58423fc8a73aa
once again), txtime branch of 'taprio_change()' is not going to
race against 'advance_sched()'. But using 'rcu_replace_pointer()'
in the former may be a good idea as well.

Suggested-by: Vinicius Costa Gomes <[e-mail]>
Signed-off-by: Dmitry Antipov <[e-mail]>
Acked-by: Vinicius Costa Gomes <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sched/sch_taprio.c

···
 			goto unlock;
 		}
 
-		rcu_assign_pointer(q->admin_sched, new_admin);
+		/* Not going to race against advance_sched(), but still */
+		admin = rcu_replace_pointer(q->admin_sched, new_admin,
+					    lockdep_rtnl_is_held());
 		if (admin)
 			call_rcu(&admin->rcu, taprio_free_sched_cb);
 	} else {