[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/ipv6/xfrm6_tunnel.c b/net/ipv6/xfrm6_tunnel.c
index fae90ff..639fe8a 100644
--- a/net/ipv6/xfrm6_tunnel.c
+++ b/net/ipv6/xfrm6_tunnel.c
@@ -319,7 +319,7 @@
 	xfrm6_tunnel_free_spi((xfrm_address_t *)&x->props.saddr);
 }
 
-static struct xfrm_type xfrm6_tunnel_type = {
+static const struct xfrm_type xfrm6_tunnel_type = {
 	.description	= "IP6IP6",
 	.owner          = THIS_MODULE,
 	.proto		= IPPROTO_IPV6,