VLAN: kill_vid is only useful for VLAN filtering devices

The interface for network device VLAN extension was confusing.
The kill_vid function is only really useful for devices that do
hardware filtering. Devices that only do VLAN receiption without
filtering were being forced to provide the hook, and there were
bugs in those devices.

Many drivers had kill_vid routine that called vlan_group_set_device, with
NULL, but that is done already.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>