gre_offload: statically build GRE offloading support

GRO/GSO layers can be enabled on a node, even if said
node is only forwarding packets.

This patch permits GSO (and upcoming GRO) support for GRE
encapsulated packets, even if the host has no GRE tunnel setup.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: H.K. Jerry Chu <hkchu@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index 2cd02f3..9138cfb 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -123,12 +123,15 @@
 	},
 };
 
-int __init gre_offload_init(void)
+static int __init gre_offload_init(void)
 {
 	return inet_add_offload(&gre_offload, IPPROTO_GRE);
 }
 
-void __exit gre_offload_exit(void)
+static void __exit gre_offload_exit(void)
 {
 	inet_del_offload(&gre_offload, IPPROTO_GRE);
 }
+
+module_init(gre_offload_init);
+module_exit(gre_offload_exit);