Android app tells you Mullvad isn't enabled if you're using tailnet lock

### What is the issue?

If you have Tailnet lock enabled and enable Mullvad exit nodes on an Android device, the app will continue to tell you that the feature needs to be enabled in the admin console.
Also there's no indication on any platform that Mullvad nodes need to be signed or are even properly working, until you realize you need to run `tailscale lock` to even see them.

And the docs are not at all clear about this, that the only way to even SEE any Mullvad nodes or know that the feature is working is via the top-level `tailscale lock`, which is a command certainly rarely ever run since the admin console gives you the `tailscale lock sign` command to copy-paste. See also https://github.com/tailscale/tailscale/issues/9103

This is a major stumbling block IMO.

### Steps to reproduce

Enable tailnet lock, enable mullbad VPN, check the exit nodes menu in Android.

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

_No response_

### OS

Android, Linux

### OS version

_No response_

### Tailscale version

latest

### Other software

_No response_

### Bug report

_No response_