mac80211: assure that certain drivers adhere to DONT_REORDER flag

Some drivers use skb->priority to determine on which queue to send
a frame. An example is mt76x2u (this was tested on an AWUS036ACM).
This means these drivers currently do not adhere to the DONT_REORDER
flag. To fix this, we do not set skb->priority based on the QoS TID
of injected frames when the DONT_REORDER flag is set.
Signed-off-by: NMathy Vanhoef <Mathy.Vanhoef@kuleuven.be>
Link: https://lore.kernel.org/r/20201104061823.197407-5-Mathy.Vanhoef@kuleuven.beSigned-off-by: NJohannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -2271,8 +2271,13 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 						    payload[7]);
 	}
 
-	/* Initialize skb->priority for QoS frames */
-	if (ieee80211_is_data_qos(hdr->frame_control)) {
+	/* Initialize skb->priority for QoS frames. If the DONT_REORDER flag
+	 * is set, stick to the default value for skb->priority to assure
+	 * frames injected with this flag are not reordered relative to each
+	 * other.
+	 */
+	if (ieee80211_is_data_qos(hdr->frame_control) &&
+	    !(info->control.flags & IEEE80211_TX_CTRL_DONT_REORDER)) {
 		u8 *p = ieee80211_get_qos_ctl(hdr);
 		skb->priority = *p & IEEE80211_QOS_CTL_TAG1D_MASK;
 	}