pub fn poll_send_to(
        &self,
        target: SocketAddr,
        addr: &Address,
        payload: &[u8],
        cx: &mut Context<'_>,
    ) -> Poll<ProxySocketResult<usize>> {
        self.poll_send_to_with_ctrl(target, addr, &DEFAULT_SOCKET_CONTROL, payload, cx)
    }
poll family functions

Send a UDP packet to addr through proxy `target`

NOTE: the `send_timeout` is ignored.
crates/shadowsocks/src/relay/udprelay/proxy_socket.rs