mlxsw: spectrum: Allocate active VLANs only for port netdevs

When adding support for bridges between VLAN interfaces, we'll introduce
a new entity called a vPort, which is a represntation of the VLAN
interface in the hardware.

The main difference between a vPort and a physical port is that several
FIDs can be bound to the latter, whereas only one (called a vFID) can be
bound to the first.

Therefore, it makes sense to use the same struct to represent the two,
but to only allocate the 'active_vlans' bitmap in case of a physical
port.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>