mac80211: Use suitable semantics for beacon availability indication

Currently beacon availability upon association is marked by have_beacon
flag of assoc_data structure that becomes unavailable when association
completes. However beacon availability indication is required also after
association to inform a driver. Currently dtim_period parameter is used
for this purpose. Move have_beacon flag to another structure, persistant
throughout a interface's life cycle. Use suitable sematics for beacon
availability indication.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
[fix another instance of BSS_CHANGED_DTIM_PERIOD in docs]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index cb37f82..a405a7a 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -217,8 +217,8 @@
  * @BSS_CHANGED_TXPOWER: TX power setting changed for this interface
  * @BSS_CHANGED_P2P_PS: P2P powersave settings (CTWindow, opportunistic PS)
  *	changed (currently only in P2P client mode, GO mode will be later)
- * @BSS_CHANGED_DTIM_PERIOD: the DTIM period value was changed (set when
- *	it becomes valid, managed mode only)
+ * @BSS_CHANGED_BEACON_INFO: Data from the AP's beacon became available:
+ *	currently dtim_period only is under consideration.
  * @BSS_CHANGED_BANDWIDTH: The bandwidth used by this interface changed,
  *	note that this is only called when it changes after the channel
  *	context had been assigned.
@@ -244,7 +244,7 @@
 	BSS_CHANGED_PS			= 1<<17,
 	BSS_CHANGED_TXPOWER		= 1<<18,
 	BSS_CHANGED_P2P_PS		= 1<<19,
-	BSS_CHANGED_DTIM_PERIOD		= 1<<20,
+	BSS_CHANGED_BEACON_INFO		= 1<<20,
 	BSS_CHANGED_BANDWIDTH		= 1<<21,
 
 	/* when adding here, make sure to change ieee80211_reconfig */
@@ -288,7 +288,7 @@
  *	IEEE80211_HW_2GHZ_SHORT_SLOT_INCAPABLE hardware flag
  * @dtim_period: num of beacons before the next DTIM, for beaconing,
  *	valid in station mode only if after the driver was notified
- *	with the %BSS_CHANGED_DTIM_PERIOD flag, will be non-zero then.
+ *	with the %BSS_CHANGED_BEACON_INFO flag, will be non-zero then.
  * @sync_tsf: last beacon's/probe response's TSF timestamp (could be old
  *	as it may have been received during scanning long ago). If the
  *	HW flag %IEEE80211_HW_TIMING_BEACON_ONLY is set, then this can