mac80211: Allow disabling SGI-20

This allows user-space (wpa_supplicant) to disable
short guard interval (SGI) for 20Mhz.  The SGI-40
disable option is already handled.
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ht.c

@@ -62,6 +62,9 @@ void ieee80211_apply_htcap_overrides(struct ieee80211_sub_if_data *sdata,
 	__check_htcap_disable(sdata, ht_cap, IEEE80211_HT_CAP_SUP_WIDTH_20_40);
 	__check_htcap_disable(sdata, ht_cap, IEEE80211_HT_CAP_SGI_40);
 
+	/* Allow user to disable SGI-20 (SGI-40 is handled above) */
+	__check_htcap_disable(sdata, ht_cap, IEEE80211_HT_CAP_SGI_20);
+
 	/* Allow user to disable the max-AMSDU bit. */
 	__check_htcap_disable(sdata, ht_cap, IEEE80211_HT_CAP_MAX_AMSDU);
 

net/mac80211/main.c

@@ -537,6 +537,7 @@ static const struct ieee80211_ht_cap mac80211_ht_capa_mod_mask = {
 
 	.cap_info = cpu_to_le16(IEEE80211_HT_CAP_SUP_WIDTH_20_40 |
 				IEEE80211_HT_CAP_MAX_AMSDU |
+				IEEE80211_HT_CAP_SGI_20 |
 				IEEE80211_HT_CAP_SGI_40),
 	.mcs = {
 		.rx_mask = { 0xff, 0xff, 0xff, 0xff, 0xff,