Nun, ich habe das Problem am Ende mit der dynamischen Interface-Option wds-mode = gelöst:
system reset-configuration interface bridge add name=bridge interface bridge port add bridge=bridge interface=wlan1 interface bridge port add bridge=bridge interface=ether1 ip address add interface=bridge address=192.168.151.11/24 ip route add gateway=192.168.151.1 interface wireless set country="germany 5.8 fixed p-p" mode=bridge ssid=ALARM-BR-BHP numbers=wlan1 interface wireless set wlan1 wds-mode=dynamic wds-default-bridge=bridge interface wireless security-profiles add name=alarm authentication-types=wpa2-psk wpa2-pre-shared-key=alarmkey interface wireless set security-profile=alarm numbers=wlan1 interface wireless enable numbers=wlan1