wifi-scripts: ucode: fix init value of config.ht_capab under 20MHz

Currently the path for setting 20MHz doesn't set ht_capab to '' at the
beginning which results in null in ht_capab in hostapd.conf.

Fix this by setting config.ht_capab to '' for 20MHz htmode.

Fixes: #20762

Signed-off-by: Zhi-Jun You <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20768
Signed-off-by: Hauke Mehrtens <[email protected]>

package/network/config/wifi-scripts/files-ucode/usr/share/ucode/wifi/hostapd.uc

@@ -150,8 +150,10 @@ function device_htmode_append(config) {
 	/* 802.11n */
 	config.ieee80211n = 0;
 	if (config.band != '6g') {
-		if (config.htmode in [ 'VHT20', 'HT20', 'HE20', 'EHT20' ])
+		if (config.htmode in [ 'VHT20', 'HT20', 'HE20', 'EHT20' ]) {
 			config.ieee80211n = 1;
+			config.ht_capab = '';
+		}
 		if (config.htmode in [ 'HT40', 'HT40+', 'HT40-', 'VHT40', 'VHT80', 'VHT160', 'HE40', 'HE80', 'HE160', 'EHT40', 'EHT80', 'EHT160' ]) {
 			config.ieee80211n = 1;
 			if (!config.channel)