scsi: core: Fix VPD LUN ID designator priorities

scsi: core: Fix VPD LUN ID designator priorities

The current implementation of scsi_vpd_lun_id() uses the designator length
as an implicit measure of priority. This works most of the time, but not
always. For example, some Hitachi storage arrays return this in VPD 0x83:

VPD INQUIRY: Device Identification page
  Designation descriptor number 1, descriptor length: 24
    designator_type: T10 vendor identification,  code_set: ASCII
    associated with the Addressed logical unit
      vendor id: HITACHI
      vendor specific: 5030C3502025
  Designation descriptor number 2, descriptor length: 6
    designator_type: vendor specific [0x0],  code_set: Binary
    associated with the Target port
      vendor specific: 08 03
  Designation descriptor number 3, descriptor length: 20
    designator_type: NAA,  code_set: Binary
    associated with the Addressed logical unit
      NAA 6, IEEE Company_id: 0x60e8
      Vendor Specific Identifier: 0x7c35000
      Vendor Specific Identifier Extension: 0x30c35000002025
      [0x60060e8007c350000030c35000002025]

The current code would use the first descriptor because it's longer than
the NAA descriptor. But this is wrong, the kernel is supposed to prefer NAA
descriptors over T10 vendor ID. Designator length should only be used to
compare designators of the same type.

This patch addresses the issue by separating designator priority and
length.

Link: https://lore.kernel.org/r/20201029170846.14786-1-mwilck@suse.com
Fixes: 9983bed3907c ("scsi: Add scsi_vpd_lun_id()")
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>