mac80211: implement STA CSA for drivers using channel contexts

Limit the current implementation to a single channel context used by
a single vif, thereby avoiding multi-vif/channel complexities.

Reuse the main function from AP CSA code, but move a portion out in
order to fit the STA scenario.

Add a new mac80211 HW flag so we don't break devices that don't support
channel switch with channel-contexts. The new behavior will be opt-in.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -1502,6 +1502,11 @@ struct ieee80211_tx_control {
  *
  * @IEEE80211_HW_TIMING_BEACON_ONLY: Use sync timing from beacon frames
  *	only, to allow getting TBTT of a DTIM beacon.
+ *
+ * @IEEE80211_HW_CHANCTX_STA_CSA: Support 802.11h based channel-switch (CSA)
+ *	for a single active channel while using channel contexts. When support
+ *	is not enabled the default action is to disconnect when getting the
+ *	CSA frame.
  */
 enum ieee80211_hw_flags {
 	IEEE80211_HW_HAS_RATE_CONTROL			= 1<<0,
@@ -1532,6 +1537,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_P2P_DEV_ADDR_FOR_INTF		= 1<<25,
 	IEEE80211_HW_TIMING_BEACON_ONLY			= 1<<26,
 	IEEE80211_HW_SUPPORTS_HT_CCK_RATES		= 1<<27,
+	IEEE80211_HW_CHANCTX_STA_CSA			= 1<<28,
 };
 
 /**