message: Android doesn't support obtaining MTU from tun fd
diff: @@ -134,13 +134,13 @@ pub struct Tun {
  impl Tun {
  pub async fn run(mut self) -> io::Result<()> {
  - let mtu = self.device.get_ref().mtu().expect("mtu");
  + if let Ok(mtu) = self.device.get_ref().mtu() {
  assert!(mtu > 0 && mtu as usize > IFF_PI_PREFIX_LEN);
  + }
  info!(
  - "shadowsocks tun device {}, mtu {}, mode {}",
  + "shadowsocks tun device {}, mode {}",
  self.device.get_ref().name(),
  - mtu,
  self.mode,
  );
  