Support ios, tvos and visionos

[mxinden]

iOS does not ship with <net/route.h>, see #82.

#83 dropped support for the Apple OS variants, see e.g. code below:

mtu/build.rs

Lines 47 to 52 in 8329753

	// Platforms currently not supported.
	//
	// See <https://github.com/mozilla/mtu/issues/82>.
	if matches!(target_os.as_str(), "ios" | "tvos" | "visionos") {
	return;
	}

mtu/src/lib.rs

Lines 101 to 107 in 8329753

	// Platforms currently not supported.
	//
	// See <https://github.com/mozilla/mtu/issues/82>.
	#[cfg(any(target_os = "ios", target_os = "tvos", target_os = "visionos"))]
	pub fn interface_and_mtu_impl(remote: IpAddr) -> Result<(String, usize)> {
	return Err(default_err());
	}

We should add support for target_os ios, tvos and visionos in the future.