scsi: target: alua: Do not report emtpy port group

The default target port group is always returned in the list of port
groups, even if the behaviour is unwanted, i.e. it has no members and
non-default port groups are primary port groups.

That violates SPC-4 "6.37 REPORT TARGET PORT GROUPS command":

  Every target port group shall contain at least one target port. The
  target port group descriptor shall include one target port descriptor for
  each target port in the target port group.

This patch hides port groups with no ports in REPORT TARGET PORT GROUPS
response.

Link: https://lore.kernel.org/r/20220912214549.27882-1-d.bogdanov@yadro.com


Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>