[Feature request] provide guest network by unix socket

I have a project called [RootlessRouter](https://github.com/KusakabeSi/RootlessRouter), recently there is a problem in this project: The VPP host stack is very unstable.
So I want to use this slirpnetstack to replace the VPP Host stack.

This slirpnetstack has `guest network` side (Layer2/Layer3) and host kernel side(Layer 4).
But the documented way to connect to `guest network` is using netns and tun/tap device, which is unavailable in a unprivileged docker container.
Is it possible to use unix socket to provide the `guest network` instead of using netns and tun/tap? Our VPN daemon just write the network stream to specific unix socket, then this `slirpnetstack` can convert received SYN from it and becomes connect() in the host kernel namespace. L3 UDP packet becomes sendto(), and so on.