net: sky2: convert to hw_features

Caveats:
 - driver modifies vlan_features on HW VLAN TX changes
 - broken RX checksum will be reenabled on features change

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