[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/esp6.c b/net/ipv6/esp6.c
index ca48c56..8e0f142 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -538,7 +538,7 @@
 	return err;
 }
 
-static struct xfrm_type esp6_type =
+static const struct xfrm_type esp6_type =
 {
 	.description	= "ESP6",
 	.owner	     	= THIS_MODULE,