igb: allow vlan devices to use TSO and TCP CSUM offload

Using the new interface for propagating device feature flags into VLAN
deivces, turn on TSO and CSUM offload on VLAN devices.

Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>