cfg80211: Remove deprecated create_singlethread_workqueue

The workqueue "cfg80211_wq" is involved in cleanup, scan and event related
works. It queues multiple work items &rdev->event_work,
&rdev->dfs_update_channels_wk,
&wiphy_to_rdev(request->wiphy)->scan_done_wk,
&wiphy_to_rdev(wiphy)->sched_scan_results_wk, which require strict
execution ordering.
Hence, an ordered dedicated workqueue has been used.

Since it's a wireless driver, WQ_MEM_RECLAIM has been set to ensure
forward progress under memory pressure.
Signed-off-by: NBhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/wireless/core.c

@@ -1252,7 +1252,7 @@ static int __init cfg80211_init(void)
 	if (err)
 		goto out_fail_reg;
 
-	cfg80211_wq = create_singlethread_workqueue("cfg80211");
+	cfg80211_wq = alloc_ordered_workqueue("cfg80211", WQ_MEM_RECLAIM);
 	if (!cfg80211_wq) {
 		err = -ENOMEM;
 		goto out_fail_wq;