qeth: convert to hw_features part 2

Set rx csum default to hw checksumming again.
Remove sysfs interface for rx csum (checksumming) and TSO (large_send).
With the new hw_features it does not work to keep the old sysfs
interface in parallel. Convert options.checksum_type to new hw_features.

Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>