net: dsa: mt7530: fix VLAN setup

Allow DSA to add VLAN entries even if VLAN filtering is disabled, so
enabling it will not block the traffic of existent ports in the bridge

Signed-off-by: DENG Qingfang <dqfext@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>