mac80211: add post_channel_switch driver operation

As a counterpart to the pre_channel_switch operation, add a
post_channel_switch operation.  This allows the drivers to go back to
a normal configuration after the channel switch is completed.

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

net/mac80211/cfg.c

@@ -2919,7 +2919,6 @@ static int __ieee80211_csa_finalize(struct ieee80211_sub_if_data *sdata)
 		return err;
 
 	ieee80211_bss_info_change_notify(sdata, changed);
-	cfg80211_ch_switch_notify(sdata->dev, &sdata->csa_chandef);
 
 	if (sdata->csa_block_tx) {
 		ieee80211_wake_vif_queues(local, sdata,
@@ -2927,6 +2926,12 @@ static int __ieee80211_csa_finalize(struct ieee80211_sub_if_data *sdata)
 		sdata->csa_block_tx = false;
 	}
 
+	err = drv_post_channel_switch(sdata);
+	if (err)
+		return err;
+
+	cfg80211_ch_switch_notify(sdata->dev, &sdata->csa_chandef);
+
 	return 0;
 }