[SCSI] zfcp: Allow midlayer to scan for LUNs when running in NPIV mode

Enable the LUN scanning mechanism in the SCSI midlayer:
- Do not set the disable_target_scan bit in the FC transport class.
- Set max_lun to 0xFFFFFFFF to allow the midlayer scan to include
  the two-level hierachical LUNs (like 0x40XX40XX00000000, but in SCSI
  midlayer LUN format).
- Set max_id to a high value to allow triggering the SCSI device
  rescan from sysfs.

When running in NPIV mode, zfcp accepts all LUNs in slave_attach. When
running in non-NPIV mode, the list of zfcp_unit structs determines
which SCSI devices are allowed on the current system.

Reviewed-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>