Duplicate IP address, and permissions problems on Windows

[Jason A. Donenfeld]

Hey David,

It's pretty typical behavior on Windows for IP addresses to be
exclusive per interface. WireGuard for Windows does something similar:
https://git.zx2c4.com/wireguard-windows/tree/tunnel/addressconfig.go#n22

With regards to permissions, you must be Local System, which is
already the case if you're running inside a service. If you'd like to
run as a mere Administrator process, you can steal a token with a
technique like https://git.zx2c4.com/wireguard-tools/tree/src/ipc-uapi-windows.h#n14
or https://git.zx2c4.com/wireguard-windows/tree/elevate/doas.go#n30

Jason