fib: Add fib rule match on tunnel id

This add the ability to select a routing table based on the tunnel
id which allows to maintain separate routing tables for each virtual
tunnel network.

ip rule add from all tunnel-id 100 lookup 100
ip rule add from all tunnel-id 200 lookup 200

A new static key controls the collection of metadata at tunnel level
upon demand.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -143,7 +143,8 @@ static struct workqueue_struct *vxlan_wq;
 
 static inline bool vxlan_collect_metadata(struct vxlan_sock *vs)
 {
-	return vs->flags & VXLAN_F_COLLECT_METADATA;
+	return vs->flags & VXLAN_F_COLLECT_METADATA ||
+	       ip_tunnel_collect_metadata();
 }
 
 #if IS_ENABLED(CONFIG_IPV6)