scsi: target: replace fabric_ops.name with fabric_alias

iscsi_target_mod is the only LIO fabric where fabric_ops.name differs from
the fabric_ops.fabric_name string.  fabric_ops.name is used when matching
target/$fabric ConfigFS create paths, so rename it .fabric_alias and
fallback to target/$fabric vs .fabric_name comparison if .fabric_alias
isn't initialised.  iscsi_target_mod is the only fabric module to set
.fabric_alias . All other fabric modules rely on .fabric_name matching and
can drop the duplicate string.

Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>