Remove android-specific codepath for getifaddrs

[jamilbk]

Remove android-specific codepath for getifaddrs

This is not supported in Android 11+. Instead, use libc getifaddr which allegedly works with Android 7+.

See messense/if-addrs#14

[jamilbk]

However, this issue on that same repo isn't very promising:

messense/if-addrs#21

[thomaseizinger]

This is only deleting code. Is there a libc fallback that gets applied automatically?

[jamilbk]

@thomaseizinger That's a good question. This ffi is only for android, but the ifaces feature's unix codepath presumably calls getifaddr as well, so it's not clear to me. I do know it compiles and seems to run fine on Android.

getifaddr is defined like this:

extern "C" {
    pub fn getifaddrs(ifap: *mut *mut ifaddrs) -> ::std::os::raw::c_int;
}

I tried using libc::getifaddrs but that triggered a massive slew of refactoring that I attempted but ultimately gave up on.

This simple crate seems to do away with the need for this ifaces feature altogether: https://github.com/messense/if-addrs but it was taking me too long to refactor to that.

So I ended up with this PR.

[jamilbk]

One more good reason to roll our own minimal STUN/TURN client and do away with webrtc entirely.

[jamilbk]

@thomaseizinger This commit is successfully passing CI here: firezone/firezone#1930

So I assume that getifaddrs in libc is found because of the extern "C" block? 🙃

[conectado]

@thomaseizinger This commit is successfully passing CI here: firezone/firezone#1930

So I assume that getifaddrs in libc is found because of the extern "C" block? 🙃

This is similar to how C/C++ does it, extern blocks are just function declarations, then as part of the compilation the linker links to the declared functions if the library is included(which is in the case of glibc)

Here I wrote an example with the write function

[conectado]

I think this looks good, we are sacrificing Android's <7 support which released 6 years ago, I think this is acceptable.