Make the ar2133ForceBias() call controllable at runtime.

At least one AR5416 user has reported measurable throughput drops
with this option. For now, disable it and make it a run-time
twiddle. It won't take affect until the next radio programming
trip though (eg channel scan, channel change.)

sys/dev/ath/ah_osdep.c

@@ -85,6 +85,11 @@ SYSCTL_INT(_hw_ath_hal, OID_AUTO, debug, CTLFLAG_RW, &ath_hal_debug,
 TUNABLE_INT("hw.ath.hal.debug", &ath_hal_debug);
 #endif /* AH_DEBUG */
 
+int ath_hal_ar5416_biasadj = 0;
+SYSCTL_INT(_hw_ath_hal, OID_AUTO, ar5416_biasadj, CTLFLAG_RW,
+	&ath_hal_debug, 0, "Enable 2ghz AR5416 direction sensitivity"
+	" bias adjust");
+
 /* NB: these are deprecated; they exist for now for compatibility */
 int	ath_hal_dma_beacon_response_time = 2;	/* in TU's */
 SYSCTL_INT(_hw_ath_hal, OID_AUTO, dma_brt, CTLFLAG_RW,

sys/dev/ath/ath_hal/ah_internal.h

@@ -476,6 +476,7 @@ isBigEndian(void)
 extern	int ath_hal_dma_beacon_response_time;	/* in TU's */
 extern	int ath_hal_sw_beacon_response_time;	/* in TU's */
 extern	int ath_hal_additional_swba_backoff;	/* in TU's */
+extern	int ath_hal_ar5416_biasadj;		/* 1 or 0 */
 
 /* wait for the register contents to have the specified value */
 extern	HAL_BOOL ath_hal_wait(struct ath_hal *, u_int reg,

sys/dev/ath/ath_hal/ar5416/ar2133.c

@@ -185,7 +185,7 @@ ar2133SetChannel(struct ath_hal *ah, const struct ieee80211_channel *chan)
 	}
 
 	/* Workaround for hw bug - AR5416 specific */
-	if (AR_SREV_OWL(ah))
+	if (AR_SREV_OWL(ah) && ath_hal_ar5416_biasadj)
 		ar2133ForceBias(ah, freq);
 
 	reg32 = (channelSel << 8) | (aModeRefSel << 2) | (bModeSynth << 1) |