Outgoing traffic from the exit node isn't routing through the VPN

### What is the issue?

Hey, weird issue, firstly I wanna say that it worked before, all until restart, or perhaps restart updated to 1.76.6?

Generally, my issue is that I have a Mac that runs a Tailscale exit node and connects to a WireGuard external VPN.
I expect that if I connect to this exit node from another device, it will inherit the IP of the external VPN and access to the Tailscale network, but that isn't the case.
Instead the other device that I connect to exit node has my current location as if I didn't connect to VPN and has access to TS network.

The PC that runs the exit node and VPN has the IP of the external VPN as intended, so connecting to the exit node should also inherit this connection.

I genuinely don't remember what I did before, but I achieved such result and it worked perfectly okay, do you have any idea how can I get it working again?

### Steps to reproduce

1. Make TS exit node on a device A
2. Connect to external VPN on device A _(Device A network is routed through external VPN as intended)_
4. Connect to exit node A from device B
5. Expecting device B to have IP of VPN that runs on exit node A
6. Instead device B has current location IP as if external VPN didn't exist. Tailscale network works though.

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

Basically restart of exit node PC, could be that it updated to 1.76.6 during that.

### OS

macOS

### OS version

15.1.1

### Tailscale version

1.76.6

### Other software

GUI Wireguard MacOS client

### Bug report

BUG-c40542bb0cc381162c5e2bc83992ba347a984184e37d089abcf5f9ad9d80b7ec-20241205175534Z-fa4375b3a2c1affa