tunnels: fix netns vs proto registration ordering

Same stuff as in ip_gre patch: receive hook can be called before netns
setup is done, oopsing in net_generic().

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 10207cc..52ffd29 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -1227,15 +1227,14 @@
 
 	printk(KERN_INFO "IPv6 over IPv4 tunneling driver\n");
 
-	if (xfrm4_tunnel_register(&sit_handler, AF_INET6) < 0) {
-		printk(KERN_INFO "sit init: Can't add protocol\n");
-		return -EAGAIN;
-	}
-
 	err = register_pernet_device(&sit_net_ops);
 	if (err < 0)
-		xfrm4_tunnel_deregister(&sit_handler, AF_INET6);
-
+		return err;
+	err = xfrm4_tunnel_register(&sit_handler, AF_INET6);
+	if (err < 0) {
+		unregister_pernet_device(&sit_net_ops);
+		printk(KERN_INFO "sit init: Can't add protocol\n");
+	}
 	return err;
 }