mlxsw: spectrum_switchdev: Do not set field when it is reserved

When configuring an FDB entry pointing to a LAG netdev (or its upper),
the driver should only set the 'lag_vid' field when the FID (filtering
identifier) is of 802.1D type.

Extend the 802.1D FID family with an attribute indicating whether this
field should be set and based on its value set the field or leave it
blank.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>