mac80211: allow tx via monitor iface when DFS

Allow send frames using monitor interface
when DFS chandef and we pass CAC (beaconing
allowed).

This fix problem when old kernel and new backports used,
in such case hostapd create/use also monitor interface.
Before this patch all frames hostapd send using monitor
iface were dropped when AP was configured on DFS channel.
Signed-off-by: NJanusz Dziedzic <janusz.dziedzic@tieto.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -1620,12 +1620,12 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 {
 	struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 	struct ieee80211_chanctx_conf *chanctx_conf;
-	struct ieee80211_channel *chan;
 	struct ieee80211_radiotap_header *prthdr =
 		(struct ieee80211_radiotap_header *)skb->data;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 	struct ieee80211_hdr *hdr;
 	struct ieee80211_sub_if_data *tmp_sdata, *sdata;
+	struct cfg80211_chan_def *chandef;
 	u16 len_rthdr;
 	int hdrlen;
 
@@ -1723,9 +1723,9 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 	}
 
 	if (chanctx_conf)
-		chan = chanctx_conf->def.chan;
+		chandef = &chanctx_conf->def;
 	else if (!local->use_chanctx)
-		chan = local->_oper_chandef.chan;
+		chandef = &local->_oper_chandef;
 	else
 		goto fail_rcu;
 
@@ -1745,10 +1745,11 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 	 * radar detection by itself. We can do that later by adding a
 	 * monitor flag interfaces used for AP support.
 	 */
-	if ((chan->flags & (IEEE80211_CHAN_NO_IR | IEEE80211_CHAN_RADAR)))
+	if (!cfg80211_reg_can_beacon(local->hw.wiphy, chandef,
+				     sdata->vif.type))
 		goto fail_rcu;
 
-	ieee80211_xmit(sdata, skb, chan->band);
+	ieee80211_xmit(sdata, skb, chandef->chan->band);
 	rcu_read_unlock();
 
 	return NETDEV_TX_OK;