net: dsa: mv88e6xxx: Fix adding vlan 0

8021q module adds vlan 0 to all interfaces when it starts.
When 8021q module is loaded it isn't possible to create bond
with mv88e6xxx interfaces, bonding module dipslay error
"Couldn't add bond vlan ids", because it tries to add vlan 0
to slave interfaces.

There is unexpected behavior in the switch. When a PVID
is assigned to a port the switch changes VID to PVID
in ingress frames with VID 0 on the port. Expected
that the switch doesn't assign PVID to tagged frames
with VID 0. But there isn't a way to change this behavior
in the switch.

Fixes: 57e661aa ("net: dsa: mv88e6xxx: Link aggregation support")
Signed-off-by: Eldar Gasanov <eldargasanov2@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -1618,9 +1618,6 @@ static int mv88e6xxx_port_check_hw_vlan(struct dsa_switch *ds, int port,
 	struct mv88e6xxx_vtu_entry vlan;
 	int i, err;
 
-	if (!vid)
-		return -EOPNOTSUPP;
-
 	/* DSA and CPU ports have to be members of multiple vlans */
 	if (dsa_is_dsa_port(ds, port) || dsa_is_cpu_port(ds, port))
 		return 0;
@@ -2109,6 +2106,9 @@ static int mv88e6xxx_port_vlan_add(struct dsa_switch *ds, int port,
 	u8 member;
 	int err;
 
+	if (!vlan->vid)
+		return 0;
+
 	err = mv88e6xxx_port_vlan_prepare(ds, port, vlan);
 	if (err)
 		return err;