no network with net_admin Capability

[felix-git-hub]

I am trying to use this docker image to run n2n vpn, the vpn needs tuntap, so the net_admin with /dev/net/tun device is needed, however openwrt docker witih net_admin can not connect to internet, the eth0 cannot get ip address, fails with static address either.
it seems /sbin/init cannot correctly config network, can anyone tell me how to config the docker image?

version: '3.1'

services:

openwrt:
image: openwrtorg/rootfs:openwrt-21.02
restart: always
container_name: openwrt
cap_add:
- NET_ADMIN
devices:
- /dev/net/tun
ports:
- 8082:80