iwlwifi: mvm: fix MCAST in AP mode

In multicast, there is no retries nor RTS since there is no
specific recipient that can ACK or send CTS. This means
that we must not use the rate scale table for multicast
frames.
This true for any frame that doesn't have a valid
ieee80211_sta pointer.
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/iwlwifi/mvm/tx.c

@@ -175,7 +175,7 @@ static void iwl_mvm_set_tx_cmd_rate(struct iwl_mvm *mvm,
 	 * table is controlled by LINK_QUALITY commands
 	 */
 
-	if (ieee80211_is_data(fc)) {
+	if (ieee80211_is_data(fc) && sta) {
 		tx_cmd->initial_rate_index = 0;
 		tx_cmd->tx_flags |= cpu_to_le32(TX_CMD_FLG_STA_RATE);
 		return;