FR: libtailscale: add function to RegisterInterfaceGetter for Android SDK30 support

### What are you trying to do?

After playing with the pre-existing apps, I have moved onto playing with the libtailscale and using in my own programs. After successfully testing echo server on Linux, I then wondered how far I would get if I tried to use it on Android. I currently have got as far as the pre-existing bug on android/go where we need to register our own network interface provided function, like you did in your own android app to work around the netlink/go issue. #2293

It doesn't look like the current libtailscale C binding exposes a function to register such a provider with interfaces.RegisterInterfaceGetter().

To be able to move forward

### How should we solve this?

Implement function to register network interface provider

### What is the impact of not solving this?

Cannot move forward due to errors on tailscale_up()

### Anything else?

https://github.com/tailscale/tailscale-android/pull/21/files