ath5k: fix slot time handling

Set the slot time based on the mac80211 short slot vs long slot setting
instead of just forcing long slot for all CCK-enabled channels.
This slightly improves 802.11g mode performance in in my tests.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath5k/mac80211-ops.c b/drivers/net/wireless/ath/ath5k/mac80211-ops.c
index 9be29b7..807bd64 100644
--- a/drivers/net/wireless/ath/ath5k/mac80211-ops.c
+++ b/drivers/net/wireless/ath/ath5k/mac80211-ops.c
@@ -282,6 +282,15 @@
 	if (changes & BSS_CHANGED_BEACON_INT)
 		sc->bintval = bss_conf->beacon_int;
 
+	if (changes & BSS_CHANGED_ERP_SLOT) {
+		int slot_time;
+
+		ah->ah_short_slot = bss_conf->use_short_slot;
+		slot_time = ath5k_hw_get_default_slottime(ah) +
+			    3 * ah->ah_coverage_class;
+		ath5k_hw_set_ifs_intervals(ah, slot_time);
+	}
+
 	if (changes & BSS_CHANGED_ASSOC) {
 		avf->assoc = bss_conf->assoc;
 		if (bss_conf->assoc)