netfilter: add and use jump label for xt_tee

Don't bother testing if we need to switch to alternate stack
unless TEE target is used.

Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/xt_TEE.c b/net/netfilter/xt_TEE.c
index 8950e79..c5d6556 100644
--- a/net/netfilter/xt_TEE.c
+++ b/net/netfilter/xt_TEE.c
@@ -251,6 +251,7 @@
 	} else
 		info->priv = NULL;
 
+	static_key_slow_inc(&xt_tee_enabled);
 	return 0;
 }
 
@@ -262,6 +263,7 @@
 		unregister_netdevice_notifier(&info->priv->notifier);
 		kfree(info->priv);
 	}
+	static_key_slow_dec(&xt_tee_enabled);
 }
 
 static struct xt_target tee_tg_reg[] __read_mostly = {