wifi: mac80211: don't allow deactivation of all links

The set_active_links API is intended for link switching, so switching
to no links at all is not supported.
Add a warning to check that.
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240129200054.e3c113f94508.Ia35f927f914bf98dd8f9350dd4f78b1d901b1c1d@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/link.c

@@ -444,6 +444,9 @@ int ieee80211_set_active_links(struct ieee80211_vif *vif, u16 active_links)
 
 	lockdep_assert_wiphy(local->hw.wiphy);
 
+	if (WARN_ON(!active_links))
+		return -EINVAL;
+
 	if (!drv_can_activate_links(local, sdata, active_links))
 		return -EINVAL;
 
@@ -472,6 +475,9 @@ void ieee80211_set_active_links_async(struct ieee80211_vif *vif,
 {
 	struct ieee80211_sub_if_data *sdata = vif_to_sdata(vif);
 
+	if (WARN_ON(!active_links))
+		return;
+
 	if (!ieee80211_sdata_running(sdata))
 		return;