The driver was relying on dsa_slave_vlan_rx_add_vid to add VLAN ID 0. After
the blamed commit, VLAN ID 0 won't be set up anymore, breaking software
bridging fallback on VLAN-unaware bridges.
Manually set up VLAN ID 0 to fix this.
Fixes: 06cfb2df7eb0 ("net: dsa: don't advertise 'rx-vlan-filter' when not needed")
Signed-off-by: DENG Qingfang <dqfext@xxxxxxxxx>