mac80211: add channel switch command and beacon callbacks

The count field in CSA must be decremented with each beacon
transmitted. This patch implements the functionality for drivers
using ieee80211_beacon_get(). Other drivers must call back manually
after reaching count == 0.

This patch also contains the handling and finish worker for the channel
switch command, and mac80211/chanctx code to allow to change a channel
definition of an active channel context.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
[small cleanups, catch identical chandef]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 4c41c11..7ca534b 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -274,6 +274,12 @@
 			if (iftype == NL80211_IFTYPE_ADHOC &&
 			    nsdata->vif.type == NL80211_IFTYPE_ADHOC)
 				return -EBUSY;
+			/*
+			 * will not add another interface while any channel
+			 * switch is active.
+			 */
+			if (nsdata->vif.csa_active)
+				return -EBUSY;
 
 			/*
 			 * The remaining checks are only performed for interfaces
@@ -804,6 +810,8 @@
 	cancel_work_sync(&local->dynamic_ps_enable_work);
 
 	cancel_work_sync(&sdata->recalc_smps);
+	sdata->vif.csa_active = false;
+	cancel_work_sync(&sdata->csa_finalize_work);
 
 	cancel_delayed_work_sync(&sdata->dfs_cac_timer_work);
 
@@ -1267,6 +1275,7 @@
 	skb_queue_head_init(&sdata->skb_queue);
 	INIT_WORK(&sdata->work, ieee80211_iface_work);
 	INIT_WORK(&sdata->recalc_smps, ieee80211_recalc_smps_work);
+	INIT_WORK(&sdata->csa_finalize_work, ieee80211_csa_finalize_work);
 
 	switch (type) {
 	case NL80211_IFTYPE_P2P_GO: