netfilter: conntrack: make protocol tracker pointers const

Doesn't change generated code, but will make it easier to eventually
make the actual trackers themselvers const.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index e3c4c6c..2833635 100644
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -579,8 +579,8 @@
 ovs_ct_find_existing(struct net *net, const struct nf_conntrack_zone *zone,
 		     u8 l3num, struct sk_buff *skb, bool natted)
 {
-	struct nf_conntrack_l3proto *l3proto;
-	struct nf_conntrack_l4proto *l4proto;
+	const struct nf_conntrack_l3proto *l3proto;
+	const struct nf_conntrack_l4proto *l4proto;
 	struct nf_conntrack_tuple tuple;
 	struct nf_conntrack_tuple_hash *h;
 	struct nf_conn *ct;