scsi: qla2xxx: Fixup locking for session deletion

Commit d8630bb9 ('Serialize session deletion by using work_lock')
tries to fixup a deadlock when deleting sessions, but fails to take into
account the locking rules. This patch resolves the situation by
introducing a separate lock for processing the GNLIST response, and
ensures that sess_lock is released before calling
qlt_schedule_sess_delete().

Cc: Himanshu Madhani <himanshu.madhani@cavium.com>
Cc: Quinn Tran <quinn.tran@cavium.com>
Fixes: d8630bb9

 ("scsi: qla2xxx: Serialize session deletion by using work_lock")
Signed-off-by: Hannes Reinecke <hare@suse.com>
Acked-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>