bridge: Fix br_should_learn to check vlan_enabled

As Toshiaki Makita pointed out, the BRIDGE_INPUT_SKB_CB will
not be initialized in br_should_learn() as that function
is called only from br_handle_local_finish().  That is
an input handler for link-local ethernet traffic so it perfectly
correct to check br->vlan_enabled here.

Reported-by: Toshiaki Makita<toshiaki.makita1@gmail.com>
Fixes: 20adfa1a bridge: Check if vlan filtering is enabled only once.
Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_vlan.c

@@ -280,7 +280,7 @@ bool br_should_learn(struct net_bridge_port *p, struct sk_buff *skb, u16 *vid)
 	struct net_port_vlans *v;
 
 	/* If filtering was disabled at input, let it pass. */
-	if (!BR_INPUT_SKB_CB(skb)->vlan_filtered)
+	if (!br->vlan_enabled)
 		return true;
 
 	v = rcu_dereference(p->vlan_info);