zfcp: bring back unit sysfs attributes for automatic LUN scan

zfcp: bring back unit sysfs attributes for automatic LUN scan

Through sysfs attributes, zfcp unit objects
provide a trigger for manual LUN recovery
and export information for problem determination.

With commit
dec75a0dc4d9334886d3895b05eda7fa4ffe7570
"[SCSI] zfcp: Allow midlayer to scan for LUNs when running in NPIV mode"
and when attaching SCSI devices through this new optional method,
no more zfcp unit objects are allocated for such SCSI devices.
Hence, the above-mentioned trigger and information were missing.

The information and context is located in SCSI transport device data since
558a6523bca2494a19934e13a1f4dff47c022ec5
"[SCSI] zfcp: Use SCSI device data zfcp_scsi_dev instead of zfcp_unit"
30fe96a2fb98f7004a741199fbd5086b8f5212cf
"[SCSI] zfcp: Add zfcp private struct as SCSI device driver data"
Hence, introduce the trigger and the information unconditionally
for all SCSI devices attached through zfcp.

We prefix the attribute names with 'zfcp_' to prevent collisions and
to avoid mix-ups such as with the common 'state' attribute.

Since some of the new attribute views do not need zfcp_port
in the ZFCP_DEFINE_SCSI_ATTR helper macro, remove zfcp_port
to avoid compiler warnings on unused variable.
It's easy to open code the conversion from zfcp_scsi_dev to zfcp_port
for the two already existing attributes hba_id and wwpn.

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Reviewed-by: Martin Peschke <mpeschke@linux.vnet.ibm.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>