qeth: use ndo_set_features callback for initial setup and recovery

This patch uses the ndo_set_features callback during normal device
startup or recovery to turn on hardware RX checksum. Patch was done
with much help from Michal Miroslaw, thx!!!

Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>