dlm: use single thread workqueues

The recent commit to use cmwq for send and recv threads
dcce240e introduced problems,
apparently due to multiple workqueue threads.  Single threads
make the problems go away, so return to that until we fully
understand the concurrency issues with multiple threads.
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/lowcomms.c

@@ -1468,15 +1468,13 @@ static void work_stop(void)
 
 static int work_start(void)
 {
-	recv_workqueue = alloc_workqueue("dlm_recv", WQ_MEM_RECLAIM |
-					 WQ_HIGHPRI | WQ_FREEZEABLE, 0);
+	recv_workqueue = create_singlethread_workqueue("dlm_recv");
 	if (!recv_workqueue) {
 		log_print("can't start dlm_recv");
 		return -ENOMEM;
 	}
 
-	send_workqueue = alloc_workqueue("dlm_send", WQ_MEM_RECLAIM |
-					 WQ_HIGHPRI | WQ_FREEZEABLE, 0);
+	send_workqueue = create_singlethread_workqueue("dlm_send");
 	if (!send_workqueue) {
 		log_print("can't start dlm_send");
 		destroy_workqueue(recv_workqueue);