[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/ah4.c b/net/ipv4/ah4.c
index d76803a..9d4555e 100644
--- a/net/ipv4/ah4.c
+++ b/net/ipv4/ah4.c
@@ -300,7 +300,7 @@
 }
 
 
-static struct xfrm_type ah_type =
+static const struct xfrm_type ah_type =
 {
 	.description	= "AH4",
 	.owner		= THIS_MODULE,