mac80211: notify driver for change in multicast rates

With drivers implementing rate control in driver or firmware
rate_control_send_low() may not get called, and thus the
driver needs to know about changes in the multicast rate.

Add and use a new BSS change flag for this.

Signed-off-by: Pradeep Kumar Chitrapu <pradeepc@codeaurora.org>
[rewrite commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 2fd59ed..d39fd68 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -302,6 +302,8 @@ struct ieee80211_vif_chanctx_switch {
  * @BSS_CHANGED_MU_GROUPS: VHT MU-MIMO group id or user position changed
  * @BSS_CHANGED_KEEP_ALIVE: keep alive options (idle period or protected
  *	keep alive) changed.
+ * @BSS_CHANGED_MCAST_RATE: Multicast Rate setting changed for this interface
+ *
  */
 enum ieee80211_bss_change {
 	BSS_CHANGED_ASSOC		= 1<<0,
@@ -329,6 +331,7 @@ enum ieee80211_bss_change {
 	BSS_CHANGED_OCB                 = 1<<22,
 	BSS_CHANGED_MU_GROUPS		= 1<<23,
 	BSS_CHANGED_KEEP_ALIVE		= 1<<24,
+	BSS_CHANGED_MCAST_RATE		= 1<<25,
 
 	/* when adding here, make sure to change ieee80211_reconfig */
 };