net: dsa: mv88e6xxx: use ports list to map port VLAN

Instead of digging into the other dsa_switch structures of the fabric
and relying too much on the dsa_to_port helper, use the new list of
switch fabric ports to define the mask of the local ports allowed to
receive frames from another port of the fabric.

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>