[SCSI] libfc: change to make remote port callback optional

Since the rport list maintenance is now done in the rport module,
the callback (and ops) are usually not necessary.

Allow rdata->ops to be left NULL if nothing needs
to be done in an event callback.

Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>