scsi: libfc: Revisit kref handling

The kref handling in fc_rport is a mess. This patch updates
the kref handling according to the following rules:

- Take a reference whenever scheduling a workqueue
- Take a reference whenever an ELS command is send
- Drop the reference at the end of the workqueue function
- Drop the reference at the end of handling ELS replies
- Take a reference when allocating an rport
- Drop the reference when removing an rport
Signed-off-by: Hannes Reinecke <hare@suse.com>
Acked-by: Johannes Thumshirn <jth@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>