bridge: Fix the way the PVID is referenced

We are using the VLAN_TAG_PRESENT bit to detect whether the PVID is
set or not at br_get_pvid(), while we don't care about the bit in
adding/deleting the PVID, which makes it impossible to forward any
incomming untagged frame with vlan_filtering enabled.

Since vid 0 cannot be used for the PVID, we can use vid 0 to indicate
that the PVID is not set, which is slightly more efficient than using
the VLAN_TAG_PRESENT.

Fix the problem by getting rid of using the VLAN_TAG_PRESENT.
Signed-off-by: NToshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Reviewed-by: NVlad Yasevich <vyasevic@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_private.h

@@ -643,9 +643,7 @@ static inline u16 br_get_pvid(const struct net_port_vlans *v)
 	 * vid wasn't set
 	 */
 	smp_rmb();
-	return (v->pvid & VLAN_TAG_PRESENT) ?
-			(v->pvid & ~VLAN_TAG_PRESENT) :
-			VLAN_N_VID;
+	return v->pvid ?: VLAN_N_VID;
 }
 
 #else