ath6kl: make mgmt_tx accept a NULL channel

cfg80211 passes a NULL channel to mgmt_tx if the frame has
to be sent on the one currently in use by the device.
Make the implementation of mgmt_tx correctly handle this
case

Cc: Nicolas Cavallari <Nicolas.Cavallari@lri.fr>
Acked-by: NKalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: NAntonio Quartulli <antonio@open-mesh.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

drivers/net/wireless/ath/ath6kl/cfg80211.c

@@ -3175,10 +3175,21 @@ static int ath6kl_mgmt_tx(struct wiphy *wiphy, struct wireless_dev *wdev,
 {
 	struct ath6kl_vif *vif = ath6kl_vif_from_wdev(wdev);
 	struct ath6kl *ar = ath6kl_priv(vif->ndev);
-	u32 id;
+	u32 id, freq;
 	const struct ieee80211_mgmt *mgmt;
 	bool more_data, queued;
 
+	/* default to the current channel, but use the one specified as argument
+	 * if any
+	 */
+	freq = vif->ch_hint;
+	if (chan)
+		freq = chan->center_freq;
+
+	/* never send freq zero to the firmware */
+	if (WARN_ON(freq == 0))
+		return -EINVAL;
+
 	mgmt = (const struct ieee80211_mgmt *) buf;
 	if (vif->nw_type == AP_NETWORK && test_bit(CONNECTED, &vif->flags) &&
 	    ieee80211_is_probe_resp(mgmt->frame_control) &&
@@ -3188,8 +3199,7 @@ static int ath6kl_mgmt_tx(struct wiphy *wiphy, struct wireless_dev *wdev,
 		 * command to allow the target to fill in the generic IEs.
 		 */
 		*cookie = 0; /* TX status not supported */
-		return ath6kl_send_go_probe_resp(vif, buf, len,
-						 chan->center_freq);
+		return ath6kl_send_go_probe_resp(vif, buf, len, freq);
 	}
 
 	id = vif->send_action_id++;
@@ -3205,17 +3215,14 @@ static int ath6kl_mgmt_tx(struct wiphy *wiphy, struct wireless_dev *wdev,
 
 	/* AP mode Power saving processing */
 	if (vif->nw_type == AP_NETWORK) {
-		queued = ath6kl_mgmt_powersave_ap(vif,
-					id, chan->center_freq,
-					wait, buf,
-					len, &more_data, no_cck);
+		queued = ath6kl_mgmt_powersave_ap(vif, id, freq, wait, buf, len,
+						  &more_data, no_cck);
 		if (queued)
 			return 0;
 	}
 
-	return ath6kl_wmi_send_mgmt_cmd(ar->wmi, vif->fw_vif_idx, id,
-					chan->center_freq, wait,
-					buf, len, no_cck);
+	return ath6kl_wmi_send_mgmt_cmd(ar->wmi, vif->fw_vif_idx, id, freq,
+					wait, buf, len, no_cck);
 }
 
 static void ath6kl_mgmt_frame_register(struct wiphy *wiphy,