'Pass a callback function that will be called when Channel.Flow is
called by the remote server. Note that newer versions of RabbitMQ
will not issue this but instead use TCP backpressure
:param callable callback: The callback function'

def add_on_flow_callback(self, callback):

    self._has_on_flow_callback = True
    self.callbacks.add(self.channel_number, spec.Channel.Flow, callback, False)
