af_key: fix netns ops ordering on module load/unload

1. After sock_register() returns, it's possible to create sockets,
   even if module still not initialized fully (blame generic module code
   for that!)
2. Consequently, pfkey_create() can be called with pfkey_net_id still not
   initialized which will BUG_ON in net_generic():
	kernel BUG at include/net/netns/generic.h:43!
3. During netns shutdown, netns ops should be unregistered after
   key manager unregistered because key manager calls can be triggered
   from xfrm_user module:

   	general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
	pfkey_broadcast+0x111/0x210 [af_key]
	pfkey_send_notify+0x16a/0x300 [af_key]
	km_state_notify+0x41/0x70
	xfrm_flush_sa+0x75/0x90 [xfrm_user]
4. Unregister netns ops after socket ops just in case and for symmetry.

Reported by Luca Tettamanti.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Tested-by: Luca Tettamanti <kronos.it@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/key/af_key.c

@@ -3794,9 +3794,9 @@ static struct pernet_operations pfkey_net_ops = {
 
 static void __exit ipsec_pfkey_exit(void)
 {
-	unregister_pernet_subsys(&pfkey_net_ops);
 	xfrm_unregister_km(&pfkeyv2_mgr);
 	sock_unregister(PF_KEY);
+	unregister_pernet_subsys(&pfkey_net_ops);
 	proto_unregister(&key_proto);
 }
 
@@ -3807,21 +3807,22 @@ static int __init ipsec_pfkey_init(void)
 	if (err != 0)
 		goto out;
 
-	err = sock_register(&pfkey_family_ops);
+	err = register_pernet_subsys(&pfkey_net_ops);
 	if (err != 0)
 		goto out_unregister_key_proto;
+	err = sock_register(&pfkey_family_ops);
+	if (err != 0)
+		goto out_unregister_pernet;
 	err = xfrm_register_km(&pfkeyv2_mgr);
 	if (err != 0)
 		goto out_sock_unregister;
-	err = register_pernet_subsys(&pfkey_net_ops);
-	if (err != 0)
-		goto out_xfrm_unregister_km;
 out:
 	return err;
-out_xfrm_unregister_km:
-	xfrm_unregister_km(&pfkeyv2_mgr);
+
 out_sock_unregister:
 	sock_unregister(PF_KEY);
+out_unregister_pernet:
+	unregister_pernet_subsys(&pfkey_net_ops);
 out_unregister_key_proto:
 	proto_unregister(&key_proto);
 	goto out;