Have tun support multiple address

The rust tun only take one address now. We'll need both v4 and v6 address to add static route on windows

rust-tun and wintun don't support settings of ipv6 addr yet, and since hard to push this feature to upstreams(at least might take plenty of time), we may extend the Device trait now, maybe in our repo, maybe in a separate crate? here is the work-around on each platform

windows: https://github.com/firezone/firezone/blob/3d8ed7f10ed596bb7fb3ca376888eb10a267bc50/rust/connlib/tunnel/src/device_channel/tun_windows.rs#L90
macos: https://github.com/meh/rust-tun/pull/91/commits/13ae6cec497d2cf63a9d7883969109cba624f57c
linux: https://github.com/rust-netlink/rtnetlink/blob/5fca904b11ba2535fdfac30bf729aa8c10c34c0d/examples/add_address.rs#L32

yeah wintun is a bit weird it does take v6 address but doesn't expose it https://github.com/nulldotblack/wintun/blob/main/src/adapter.rs#L306

i think we can fork the rust-tun(or tun2?) and add v6 support in a separate repo and try to add it back to the upstream after we validated it's working

oh, i forgot that we are currently using the forked rust-tun. yeah, that's workable

Welcome to use tun-rs, which is actively maintained.

Watfaq / clash-rs

Have tun support multiple address #579