X540 supports SCTP checksum offload so enable it.  It was overlooked when X540
support was initially added to the driver.
Signed-off-by: NDon Skidmore <donald.c.skidmore@intel.com>
Tested-by: NEvan Swanson <evan.swanson@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>