Bug fixed:Sometimes the server won't recieved a message but tupdump can catch that. #106

func ListenUDPAndServe(log *zap.Logger, serverNet, laddr string, u *server.Updater) error {
	var (
		c   net.PacketConn
		err error
	)
	opt := u.Get()
	if reuseport.Available() && opt.ReusePort {
		c, err = reuseport.ListenPacket(serverNet, laddr)
		if err != nil {
			// Trying to listen without reuseport.
			// Sometimes reuseport.Available() can be true, but for subset
			// of interfaces it is not available.
			reusePortErr := err
			c, err = net.ListenPacket(serverNet, laddr)
			if err == nil {
				opt.ReusePort = false
				log.Warn("failed to use REUSEPORT, falling back to non-reuseport", zap.Error(reusePortErr))
			}
		}
	} else {
		c, err = net.ListenPacket(serverNet, laddr)
	}
	if err != nil {
		return err
	}
	opt.Conn = c
	s, err := server.New(opt)
	if err != nil {
		return err
	}
	u.Subscribe(s)
	return s.Serve()
}

func (s *Server) Serve() error {
	s.start()
	// ++++++++++++
	if s.reusePort {
		go s.worker(s.conn)
	}
	// +++++++++++++
	for i := 0; i < runtime.GOMAXPROCS(-1); i++ {
		s.wg.Add(1)
		if s.reusePort {
			s.log.Debug("reusing port for worker", zap.Int("w", i))
			laddr := s.conn.LocalAddr()
			conn, err := reuseport.ListenPacket(laddr.Network(), laddr.String())
			if err != nil {
				s.log.Warn("failed to listen for additional socket")
				conn = s.conn
			} else {
				s.conns = append(s.conns, conn)
			}
			go s.worker(conn)
		} else {
			go s.worker(s.conn)
		}
	}
	s.wg.Wait()
	return nil
}