Make fallback from HT40 to HT20 work

Ensure that if it is not possible to configure an allowed 20 MHz
channel pair, hostapd falls back to a single 20 MHz channel.

Signed-off-by: Eduardo Abinader <eabinader@ocedo.com>

src/ap/hw_features.c

@@ -329,6 +329,7 @@ static void ieee80211n_check_scan(struct hostapd_iface *iface)
 	res = ieee80211n_allowed_ht40_channel_pair(iface);
 	if (!res) {
 		iface->conf->secondary_channel = 0;
+		res = 1;
 		wpa_printf(MSG_INFO, "Fallback to 20 MHz");
 	}