cfg80211/mac80211: allow any interface to send channel switch notifications

For multi-vif channel switches, we want to send
NL80211_CMD_CH_SWITCH_NOTIFY to the userspace to let it decide whether
other interfaces need to be moved as well.  This is needed when we
want a P2P GO interface to follow the channel of a station, for
example.

Modify the code so that all interfaces can send CSA notifications.
Additionally, send notifications for STA CSA as well.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mlme.c

@@ -1049,6 +1049,8 @@ static void ieee80211_chswitch_post_beacon(struct ieee80211_sub_if_data *sdata)
 		sdata->csa_block_tx = false;
 	}
 
+	cfg80211_ch_switch_notify(sdata->dev, &sdata->reserved_chandef);
+
 	sdata->vif.csa_active = false;
 	ifmgd->csa_waiting_bcn = false;