igb/igbvf: set rx csum always enabled in hw, disable via sw

An issue was found in which rx checksum could not be enabled without
resetting the interface.  The issue was the hardware enable was not being
done via ethtool.  To resolve this issue and prevent conflicts with VF
configuration we will leave the feature always enabled in hardware, and
then in software we will choose to ignore the results via a sw flag.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>