message: nix Errno can be converted to i32 directly since 0.22
diff: @@ -221,11 +221,7 @@ impl PacketFilter {
  pnl.direction = ffi::PF_OUT as u8;
  if let Err(err) = ffi::ioc_natlook(self.fd, &mut pnl as *mut _) {
  - let nerr = match err.as_errno() {
  - Some(errno) => Error::from_raw_os_error(errno as i32),
  - None => Error::new(ErrorKind::Other, "ioctl DIOCNATLOOK"),
  - };
  - return Err(nerr);
  + return Err(Error::from_raw_os_error(err as i32));
  }
  let (_, dst_addr) = SockAddr::init(|dst_addr, addr_len| {
  