hostapd: fix a race condition on adding AP mode wds sta interfaces

hostapd: fix a race condition on adding AP mode wds sta interfaces

Both hostapd and netifd attempt to add a VLAN device to a bridge.
Depending on which one wins the race, bridge vlan settings might be incomplete,
or hostapd might run into an error and refuse to service the client.
Fix this by preventing hostapd from adding interfaces to the bridge and
instead rely entirely on netifd handling this properly

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