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_cbq.c b/net/sched/sch_cbq.c
index a99e37e..3a9569a 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -1635,7 +1635,8 @@
 #endif
 		}
 		sch_tree_lock(sch);
-		*old = xchg(&cl->q, new);
+		*old = cl->q;
+		cl->q = new;
 		qdisc_tree_decrease_qlen(*old, (*old)->q.qlen);
 		qdisc_reset(*old);
 		sch_tree_unlock(sch);
@@ -1776,8 +1777,8 @@
 			cbq_deactivate_class(cl);
 
 		if (rtab) {
-			rtab = xchg(&cl->R_tab, rtab);
-			qdisc_put_rtab(rtab);
+			qdisc_put_rtab(cl->R_tab);
+			cl->R_tab = rtab;
 		}
 
 		if (tb[TCA_CBQ_LSSOPT])