openvswitch: Restructure datapath.c and flow.c

Over the time datapath.c and flow.c has became pretty large files.
Following patch restructures functionality of component into three
different components:

flow.c: contains flow extract.
flow_netlink.c: netlink flow api.
flow_table.c: flow table api.

This patch restructures code without changing logic.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>

net/openvswitch/Makefile

@@ -9,6 +9,8 @@ openvswitch-y := \
 	datapath.o \
 	dp_notify.o \
 	flow.o \
+	flow_netlink.o \
+	flow_table.o \
 	vport.o \
 	vport-internal_dev.o \
 	vport-netdev.o