On Yukon FE, occasional hardware receive checksum errors are seen.
An early indication of the problem is single bit differences in the two
checksum engines.  Use this as a detection mechanism to turn off Rx
checksumming.
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NJeff Garzik <jeff@garzik.org>