net: dsa: rtl8366: Drop custom VLAN set-up

This hacky default VLAN setup was done in order to direct
packets to the right ports and provide port isolation, both
which we now support properly using custom tags and proper
bridge port isolation.

We can drop the custom VLAN code and leave all VLAN handling
alone, as users expect things to be. We can also drop
ds->configure_vlan_while_not_filtering = false; and let
the core deal with any VLANs it wants.

Cc: Mauri Sandberg <sandberg@mailfence.com>
Cc: DENG Qingfang <dqfext@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>