ath9k: fix handling of rate control probe frames

The ath9k aggregation code was already checking the rate control probe flag
to prevent starting an aggregate frame with a sampling rate. What was missing
was closing an aggregate before adding a probing frame to it.
Without that, rate control cannot have precise control over probing, which
delays using faster rates when the channel conditions improve.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -673,6 +673,7 @@ static enum ATH_AGGR_STATUS ath_tx_form_aggr(struct ath_softc *sc,
 	u16 aggr_limit = 0, al = 0, bpad = 0,
 		al_delta, h_baw = tid->baw_size / 2;
 	enum ATH_AGGR_STATUS status = ATH_AGGR_DONE;
+	struct ieee80211_tx_info *tx_info;
 
 	bf_first = list_first_entry(&tid->buf_q, struct ath_buf, list);
 
@@ -699,6 +700,11 @@ static enum ATH_AGGR_STATUS ath_tx_form_aggr(struct ath_softc *sc,
 			break;
 		}
 
+		tx_info = IEEE80211_SKB_CB(bf->bf_mpdu);
+		if (nframes && ((tx_info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE) ||
+			!(tx_info->control.rates[0].flags & IEEE80211_TX_RC_MCS)))
+			break;
+
 		/* do not exceed subframe limit */
 		if (nframes >= min((int)h_baw, ATH_AMPDU_SUBFRAME_DEFAULT)) {
 			status = ATH_AGGR_LIMITED;