[XFRM]: constify 'struct xfrm_type'

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/xfrm4_tunnel.c b/net/ipv4/xfrm4_tunnel.c
index 3268451..87f77e4 100644
--- a/net/ipv4/xfrm4_tunnel.c
+++ b/net/ipv4/xfrm4_tunnel.c
@@ -38,7 +38,7 @@
 {
 }
 
-static struct xfrm_type ipip_type = {
+static const struct xfrm_type ipip_type = {
 	.description	= "IPIP",
 	.owner		= THIS_MODULE,
 	.proto	     	= IPPROTO_IPIP,