Currently we do not implement VLAN tagging for rtl8139(C+),
still data is read from ring buffer headers.

- augment unused assignment with TODO item
- cast txdw1 to void for now
Signed-off-by: NIgor V. Kovalenko <igor.v.kovalenko@gmail.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>