mac80211: treat minstrel success probabilities below 10% as implausible

Based on minstrel_ht this patch treats success probabilities below 10% as
implausible values for throughput calculation in minstrel's statistics.
Current throughput per rate with such a low success probability is reset
to 0 MBit/s.
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rc80211_minstrel.c

@@ -92,7 +92,6 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 			mr->probability = minstrel_ewma(mr->probability,
 							mr->cur_prob,
 							EWMA_LEVEL);
-			mr->cur_tp = mr->probability * (1000000 / usecs);
 		} else
 			mr->sample_skipped++;
 
@@ -101,6 +100,12 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 		mr->success = 0;
 		mr->attempts = 0;
 
+		/* Update throughput per rate, reset thr. below 10% success */
+		if (mr->probability < MINSTREL_FRAC(10, 100))
+			mr->cur_tp = 0;
+		else
+			mr->cur_tp = mr->probability * (1000000 / usecs);
+
 		/* Sample less often below the 10% chance of success.
 		 * Sample less often above the 95% chance of success. */
 		if (mr->probability > MINSTREL_FRAC(95, 100) ||