'Gets the channels from each extension.
Merges them to create a list of channels
to hop.
:param self: An ExtensionManager object
:type self: ExtensionManager
:return: None
:rtype: None'

def get_channels(self):

    for extension in self._extensions:
        channels_interested = extension.send_channels()
        number_of_channels = len(channels_interested)
        if (channels_interested and (number_of_channels > 0)):
            self._channels_to_hop += list((set(channels_interested) - set(self._channels_to_hop)))
