openvswitch: refactor ovs flow extract API.

OVS flow extract is called on packet receive or packet
execute code path.  Following patch defines separate API
for extracting flow-key in packet execute code path.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Andy Zhou <azhou@nicira.com>
diff --git a/net/openvswitch/flow_netlink.h b/net/openvswitch/flow_netlink.h
index 4401510..206e45a 100644
--- a/net/openvswitch/flow_netlink.h
+++ b/net/openvswitch/flow_netlink.h
@@ -42,8 +42,8 @@
 
 int ovs_nla_put_flow(const struct sw_flow_key *,
 		     const struct sw_flow_key *, struct sk_buff *);
-int ovs_nla_get_flow_metadata(struct sw_flow *flow,
-			      const struct nlattr *attr);
+int ovs_nla_get_flow_metadata(const struct nlattr *, struct sw_flow_key *);
+
 int ovs_nla_get_match(struct sw_flow_match *match,
 		      const struct nlattr *,
 		      const struct nlattr *);