scsi: iscsi: Use system_unbound_wq for destroy_work
Use the system_unbound_wq for async session destruction. We don't need a
dedicated workqueue for async session destruction because:
1. perf does not seem to be an issue since we only allow 1 active work.
2. it does not have deps with other system works and we can run them in
parallel with each other.
Link: https://lore.kernel.org/r/20210525181821.7617-6-michael.christie@oracle.com
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>