via-velocity: fix vlan receipt

- vlans were using a single CAM register (see mac_set_vlan_cam)
- setting the address filtering registers for vlans is not
  needed when there is no vlan

The non-tagged interface is filtered out as soon as a tagged
(!= 0) interface is created. Its traffic appears again when an
zero-tagged interface is created.

Tested on Via Epia SN (VT6130 chipset) with several vlans whose
tag was above or beyond 255.

Signed-off-by: Séguier Régis <rseguier@e-teleport.net>
Acked-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>