sky2: FE+ vlan workaround

The FE+ workaround means the driver can no longer trust the status register
to indicate VLAN tagged frames.  The fix for this is to just disable VLAN
acceleration for that chip version. Tested and works fine.

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