wifi-scripts: let netifd alone add WDS station interfaces to the bridge

Commit da4be02fcd ("hostapd: fix a race condition on adding AP mode
wds sta interfaces") made netifd the only process that adds WDS station
interfaces to the bridge. Its hostapd patch 711 copies bridge into
wds_bridge when it parses bridge= and wds_bridge is still empty, and
hostapd.sh writes an empty wds_bridge= after bridge=.

ap.uc does not write the empty wds_bridge=, so hostapd adds each WDS
station interface to the bridge, and netifd adds it again. The commit
above names the effects of the race: incomplete bridge vlan settings,
or a client that hostapd refuses.

Write an empty wds_bridge= for a BSS with a bridge, as hostapd.sh does.
The line must follow bridge=, because patch 711 fills an empty
wds_bridge at parse time; append_vars() writes bridge first. A
wds_bridge that the config sets for a wds BSS still applies, as in
mac80211.sh.

The previous change makes netifd link WDS station interfaces that
appeared while it had no data for their vif.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -39,6 +39,11 @@ function iface_setup(config, phy, num_global_macaddr, macaddr_base) {
 	else
 		config.wds_sta = true;
 
+	/* hostapd copies bridge= into an empty wds_bridge, so wds_bridge= must
+	 * follow bridge= in append_vars() */
+	if (config.bridge)
+		set_default(config, 'wds_bridge', '');
+
 	if (!config.idx)
 		append('interface', config.ifname);
 	else