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 --cc net/openvswitch/datapath.c
Simple merge

diff --cc net/openvswitch/datapath.h
Simple merge

diff --cc net/openvswitch/flow.c
Simple merge

diff --cc net/openvswitch/flow.h
Simple merge

diff --cc net/openvswitch/flow_netlink.c
Simple merge

diff --cc net/openvswitch/flow_netlink.h
Simple merge

diff --cc net/openvswitch/vport.c
Simple merge