netfilter: nf_conntrack: register pernet subsystem before register L4 proto

In (c296bb4 netfilter: nf_conntrack: refactor l4proto support for netns)
the l4proto gre/dccp/udplite/sctp registration happened before the pernet
subsystem, which is wrong.

Register pernet subsystem before register L4proto since after register
L4proto, init_conntrack may try to access the resources which allocated
in register_pernet_subsys.

Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nf_conntrack_proto_gre.c b/net/netfilter/nf_conntrack_proto_gre.c
index bd7d01d..155ce9f8 100644
--- a/net/netfilter/nf_conntrack_proto_gre.c
+++ b/net/netfilter/nf_conntrack_proto_gre.c
@@ -420,18 +420,18 @@
 {
 	int ret;
 
-	ret = nf_ct_l4proto_register(&nf_conntrack_l4proto_gre4);
-	if (ret < 0)
-		goto out_gre4;
-
 	ret = register_pernet_subsys(&proto_gre_net_ops);
 	if (ret < 0)
 		goto out_pernet;
 
+	ret = nf_ct_l4proto_register(&nf_conntrack_l4proto_gre4);
+	if (ret < 0)
+		goto out_gre4;
+
 	return 0;
-out_pernet:
-	nf_ct_l4proto_unregister(&nf_conntrack_l4proto_gre4);
 out_gre4:
+	unregister_pernet_subsys(&proto_gre_net_ops);
+out_pernet:
 	return ret;
 }