net: s2io: convert to hw_features

This removes advertising HW_CSUM as driver does not support it.

Note: driver advertises TSO6 but not IPV6_CSUM - bug maybe?

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