[NETFILTER]: nf_conntrack_extend: use __read_mostly for struct nf_ct_ext_type

Also make them static.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/nf_nat_core.c

@@ -623,7 +623,7 @@ static void nf_nat_move_storage(struct nf_conn *conntrack, void *old)
 	write_unlock_bh(&nf_nat_lock);
 }
 
-struct nf_ct_ext_type nat_extend = {
+static struct nf_ct_ext_type nat_extend __read_mostly = {
 	.len		= sizeof(struct nf_conn_nat),
 	.align		= __alignof__(struct nf_conn_nat),
 	.destroy	= nf_nat_cleanup_conntrack,

net/netfilter/nf_conntrack_helper.c

@@ -145,7 +145,7 @@ void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 
-struct nf_ct_ext_type helper_extend = {
+static struct nf_ct_ext_type helper_extend __read_mostly = {
 	.len	= sizeof(struct nf_conn_help),
 	.align	= __alignof__(struct nf_conn_help),
 	.id	= NF_CT_EXT_HELPER,