ath9k: make beacon timer initialization more reliable

When starting the AP beacon timer, it assumes that the TSF has recently
been cleared. Set the SC_OP_TSF_RESET flag to ensure that this is always
the case.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -517,6 +517,7 @@ static void ath_beacon_config_ap(struct ath_softc *sc,
 	/* Set the computed AP beacon timers */
 
 	ath9k_hw_disable_interrupts(ah);
+	sc->sc_flags |= SC_OP_TSF_RESET;
 	ath9k_beacon_init(sc, nexttbtt, intval);
 	sc->beacon.bmisscnt = 0;
 	ath9k_hw_set_interrupts(ah, ah->imask);