net: convert sunhme/sungem network drivers to hw_features

Side effects:
 - TX offloads (HW csum, scatter-gather) can be toggled now
 - RX checksum is reported correctly now (it's always active)

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>