openvswitch: Add Kconfig dependency on GRE-DEMUX.

Openvswitch uses function from NET_IPGRE_DEMUX module.
Add Kconfig dependency to fix following compilation errors:
http://marc.info/?l=linux-netdev&m=137244035226634

CC: Jesse Gross <jesse@nicira.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Pravin Shelar <pshelar@nicira.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/openvswitch/Kconfig

@@ -19,8 +19,6 @@ config OPENVSWITCH
 	  which is able to accept configuration from a variety of sources and
 	  translate it into packet processing rules.
 
-	  Open vSwitch GRE support depends on CONFIG_NET_IPGRE_DEMUX.
-
 	  See http://openvswitch.org for more information and userspace
 	  utilities.
 
@@ -28,3 +26,17 @@ config OPENVSWITCH
 	  called openvswitch.
 
 	  If unsure, say N.
+
+config OPENVSWITCH_GRE
+	bool "Open vSwitch GRE tunneling support"
+	depends on INET
+	depends on OPENVSWITCH
+	depends on NET_IPGRE_DEMUX && !(OPENVSWITCH=y && NET_IPGRE_DEMUX=m)
+	default y
+	---help---
+	  If you say Y here, then the Open vSwitch will be able create GRE
+	  vport.
+
+	  Say N to exclude this support and reduce the binary size.
+
+	  If unsure, say Y.

net/openvswitch/vport-gre.c

@@ -16,7 +16,7 @@
  * 02110-1301, USA
  */
 
-#if IS_ENABLED(CONFIG_NET_IPGRE_DEMUX)
+#ifdef CONFIG_OPENVSWITCH_GRE
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/if.h>
@@ -271,4 +271,5 @@ const struct vport_ops ovs_gre_vport_ops = {
 	.get_name	= gre_get_name,
 	.send		= gre_tnl_send,
 };
-#endif
+
+#endif /* OPENVSWITCH_GRE */

net/openvswitch/vport.c

@@ -39,7 +39,7 @@ static const struct vport_ops *vport_ops_list[] = {
 	&ovs_netdev_vport_ops,
 	&ovs_internal_vport_ops,
 
-#if IS_ENABLED(CONFIG_NET_IPGRE_DEMUX)
+#ifdef CONFIG_OPENVSWITCH_GRE
 	&ovs_gre_vport_ops,
 #endif
 };