wifi: mac80211: handle debugfs when switching to/from MLO

In MLO, we have a per-link debugfs directory which contains the
per-link files. In case of non-MLO we would like to put the per-link
files in the netdev directory to keep it how it was before MLO.

- Upon interface creation the netdev will be created with the per-link
  files in it.
- Upon switching to MLO: delete the entire netdev directory and then
  recreate it without the per-link files. Then the per-link directories
  with the per-link files in it will be created in ieee80211_link_init()
- Upon switching to non-MLO: delete the entire netdev directory
  (including the per-link directories) and recreate it with the per-link
  files in it.

Note that this also aligns to always call the vif link debugfs
method for the deflink as promised in the documentation, which
wasn't done before.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230928172905.082e698caca9.I5bef7b2026e0f58b4a958b3d1f459ac5baeccfc9@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/link.c

@@ -235,6 +235,9 @@ static int ieee80211_vif_update_links(struct ieee80211_sub_if_data *sdata,
 		RCU_INIT_POINTER(sdata->vif.link_conf[link_id], NULL);
 	}
 
+	if (!old_links)
+		ieee80211_debugfs_recreate_netdev(sdata, true);
+
 	/* link them into data structures */
 	for_each_set_bit(link_id, &add, IEEE80211_MLD_MAX_NUM_LINKS) {
 		WARN_ON(!use_deflink &&
@@ -261,6 +264,8 @@ static int ieee80211_vif_update_links(struct ieee80211_sub_if_data *sdata,
 					   old_links & old_active,
 					   new_links & sdata->vif.active_links,
 					   old);
+		if (!new_links)
+			ieee80211_debugfs_recreate_netdev(sdata, false);
 	}
 
 	if (ret) {