wifi: mac80211: fix check for unusable RX result

If we just check "result & RX_DROP_UNUSABLE", this really only works
by accident, because SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE got to
have the value 1, and SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR is 2.

Fix this to really check the entire subsys mask for the value, so it
doesn't matter what the subsystem value is.

Fixes: 7f4e09700b ("wifi: mac80211: report all unusable beacon frames")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/drop.h

@@ -53,4 +53,7 @@ enum mac80211_drop_reason {
 #undef DEF
 };
 
+#define RX_RES_IS_UNUSABLE(result)	\
+	(((__force u32)(result) & SKB_DROP_REASON_SUBSYS_MASK) == ___RX_DROP_UNUSABLE)
+
 #endif /* MAC80211_DROP_H */

net/mac80211/rx.c

@@ -2112,7 +2112,7 @@ ieee80211_rx_h_decrypt(struct ieee80211_rx_data *rx)
 	/* either the frame has been decrypted or will be dropped */
 	status->flag |= RX_FLAG_DECRYPTED;
 
-	if (unlikely(ieee80211_is_beacon(fc) && (result & RX_DROP_UNUSABLE) &&
+	if (unlikely(ieee80211_is_beacon(fc) && RX_RES_IS_UNUSABLE(result) &&
 		     rx->sdata->dev))
 		cfg80211_rx_unprot_mlme_mgmt(rx->sdata->dev,
 					     skb->data, skb->len);