ath9k: trigger nfcal only after multiple missed beacons in AP mode

Single missed (i.e. not transmitted) beacons in AP mode are not very rare
and not necessarily an indicator of strong interference, so only trigger
noise floor recalibration when multiple consecutive beacons could not
be transmitted.
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/beacon.c

@@ -368,7 +368,8 @@ void ath_beacon_tasklet(unsigned long data)
 				"missed %u consecutive beacons\n",
 				sc->beacon.bmisscnt);
 			ath9k_hw_stop_dma_queue(ah, sc->beacon.beaconq);
-			ath9k_hw_bstuck_nfcal(ah);
+			if (sc->beacon.bmisscnt > 3)
+				ath9k_hw_bstuck_nfcal(ah);
 		} else if (sc->beacon.bmisscnt >= BSTUCK_THRESH) {
 			ath_dbg(common, ATH_DBG_BSTUCK,
 				"beacon is officially stuck\n");