net: add CONFIG_NET_INGRESS to enable ingress filtering

This new config switch enables the ingress filtering infrastructure that is
controlled through the ingress_needed static key. This prepares the
introduction of the Netfilter ingress hook that resides under this unique
static key.

Note that CONFIG_SCH_INGRESS automatically selects this, that should be no
problem since this also depends on CONFIG_NET_CLS_ACT.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index af54906..a5ef900 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1630,7 +1630,7 @@
 }
 EXPORT_SYMBOL(call_netdevice_notifiers);
 
-#ifdef CONFIG_NET_CLS_ACT
+#ifdef CONFIG_NET_INGRESS
 static struct static_key ingress_needed __read_mostly;
 
 void net_inc_ingress_queue(void)
@@ -3798,13 +3798,14 @@
 	}
 
 skip_taps:
-#ifdef CONFIG_NET_CLS_ACT
+#ifdef CONFIG_NET_INGRESS
 	if (static_key_false(&ingress_needed)) {
 		skb = handle_ing(skb, &pt_prev, &ret, orig_dev);
 		if (!skb)
 			goto unlock;
 	}
-
+#endif
+#ifdef CONFIG_NET_CLS_ACT
 	skb->tc_verd = 0;
 ncls:
 #endif