[SCSI] sd: Export effective protection mode in sysfs

Create a sysfs entry that reports the negotiated DIX/DIF protection mode
for a SCSI disk. This depends on the protection type the disk is
formatted with as well as the protection capabilities advertised by the
controller.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>