[SCSI] fcoe: fcoe fc crc offload indication by skb->ip_summed

If LLD supports FCCRC offload, it should set ip_summed to be
CHECKSUM_UNNECESSARY so we don't have to do CRC check again.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>