pkt_sched: remove unnecessary xchg() in packet schedulers

The use of xchg() hasn't been necessary since 2.2.something when proper
locking was added to packet schedulers.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_dsmark.c b/net/sched/sch_dsmark.c
index 3f9427a..d303daa 100644
--- a/net/sched/sch_dsmark.c
+++ b/net/sched/sch_dsmark.c
@@ -68,7 +68,8 @@
 	}
 
 	sch_tree_lock(sch);
-	*old = xchg(&p->q, new);
+	*old = p->q;
+	p->q = new;
 	qdisc_tree_decrease_qlen(*old, (*old)->q.qlen);
 	qdisc_reset(*old);
 	sch_tree_unlock(sch);