sky2: convert to new VLAN model (v0.2)

This converts sky2 to new VLAN offload flags control via ethtool.
It also allows for transmit offload of vlan tagged frames which
was not possible before.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Reviewed-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>