net: Define accessors to manipulate QDISC_STATE_RUNNING

Define three helpers to manipulate QDISC_STATE_RUNNIG flag, that a
second patch will move on another location.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 9d4d87c..d9549af 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -95,7 +95,7 @@
 
 static inline void qdisc_run(struct Qdisc *q)
 {
-	if (!test_and_set_bit(__QDISC_STATE_RUNNING, &q->state))
+	if (qdisc_run_begin(q))
 		__qdisc_run(q);
 }