On reset, the PVID of all ports is set to 1; if this is reset to 0,
the special cases for VLAN 1 are no longer required.
port_vlan_add is called with vid=0 when the DSA port interfaces are
enabled with no VLAN; previously the VLAN was not configured in this
case, relying on VLAN 1 being present, but with the PVID set to 0,
configuring VLAN 0 as normal works as expected.
Signed-off-by: Thomas Nixon <tom@tomn.co.uk>
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