def goaway(error_type = :no_error, message = "")
      last_id = @max_stream_ids.max
      send_immediately Frame::Goaway.new(last_id, error_type, message)
    end
def goaway(error_type = :no_error, message = "")
      last_id = @max_stream_ids.max
      send_immediately Frame::Goaway.new(last_id, error_type, message)
    end
Sends GOAWAY frame to the peer and closes the connection.
 @param error_type [Symbol] The error type to be contained in the GOAWAY frame.