cfg80211/mac80211: improve ad-hoc multicast rate handling

- store the multicast rate as an index instead of the rate value
  (reduces cpu overhead in a hotpath)
- validate the rate values (must match a bitrate in at least one sband)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/cfg80211.h

@@ -923,7 +923,7 @@ struct cfg80211_disassoc_request {
  * @privacy: this is a protected network, keys will be configured
  *	after joining
  * @basic_rates: bitmap of basic rates to use when creating the IBSS
- * @mcast_rate: multicast tx rate (in 100 kbps)
+ * @mcast_rate: per-band multicast rate index + 1 (0: disabled)
  */
 struct cfg80211_ibss_params {
 	u8 *ssid;
@@ -935,7 +935,7 @@ struct cfg80211_ibss_params {
 	u32 basic_rates;
 	bool channel_fixed;
 	bool privacy;
-	int mcast_rate;
+	int mcast_rate[IEEE80211_NUM_BANDS];
 };
 
 /**