qeth: change checksumming default for HiperSockets

Deactivate inbound checksumming on HiperSocket is a valid but
dangerous optimization in case the frame is routed from an OSA
network to an HiperSockets network. To go for sure we change the
default to software checksumming.

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