Debugging issue for a Enigma2 device

### What is the issue?

I am trying to use Tailscale on an embedded Enigma2 device (for others it is working, https://github.com/tailscale/tailscale/issues/1291)

I am starting tailscaled with tun argument:

`root@vuzero4k:~# ./tailscaled -tun userspace-networking`

**Log:**

https://pastebin.com/raw/AsbsLwCR

Now I bring up tailscale:

`root@vuzero4k:~# tailscale up --exit-node 100.6 --exit-node-allow-lan-access`

```
root@vuzero4k:~# ./tailscale status
100. vuzero4k @ linux -
100.6 adrianeu @ linux idle; exit node
```

Ifconfig doesn't show new tun interface and internet is not routed trough exit node. Ip route doesn't show any new routes.

Tun module is loaded:

```
root@vuzero4k:~# lsmod
Module Size Used by
tun 18048 0
```

Pinging my exit node:

```
root@vuzero4k:~# ./tailscale ping 100.6
pong from adeu (100.6) via DERP(fra) in 54ms
pong from adeu (100.6) via DERP(fra) in 47ms
pong from adeu (100.6) via 1......55:41641 in 37ms
```

### Steps to reproduce

_No response_

### Are there any recent changes that introduced the issue?

_No response_

### OS

Linux, Other

### OS version

_No response_

### Tailscale version

all

### Other software

_No response_

### Bug report

BUG-bd88d9a0c566c59418c27de3a6e959f600aff91a65f9af877a14397be05fef92-20230831065649Z-e49a2494b4934a6c