openvswitch: Add gre tunnel support.

Add gre vport implementation.  Most of gre protocol processing
is pushed to gre module. It make use of gre demultiplexer
therefore it can co-exist with linux device based gre tunnels.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/openvswitch/Makefile b/net/openvswitch/Makefile
index 15e7384..01bddb2 100644
--- a/net/openvswitch/Makefile
+++ b/net/openvswitch/Makefile
@@ -10,5 +10,6 @@
 	dp_notify.o \
 	flow.o \
 	vport.o \
+	vport-gre.o \
 	vport-internal_dev.o \
-	vport-netdev.o \
+	vport-netdev.o