net: sched: export an api to enable/disable flow on sch

Export a function from sch_api.c that will look up
desired qdisc and call it's registered change function
to enable/disable flow.

Change-Id: I5b6dc7a6fd2b09b796c92b3770ba83423d19c864
CRs-Fixed: 355156
Acked-by: Jimi Shah <jimis@qualcomm.com>
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>
(cherry picked from commit b8419fe690053b76658d49565c57ac654faf2eaa)
(cherry picked from commit 3a30e7aa4487f56a74f12c12f11cece6ce1f2100)
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index fffdc60..95ec28b 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -103,7 +103,8 @@
 			      struct tcf_result *res);
 extern int tc_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 		       struct tcf_result *res);
-
+extern void tc_qdisc_flow_control(struct net_device *dev, u32 tcm_handle,
+				  int flow_enable);
 /* Calculate maximal size of packet seen by hard_start_xmit
    routine of this device.
  */