'Set bridge controllers connection mode.
:param connection_mode: "out-of-band" or "in-band"'

def set_controllers_connection_mode(self, connection_mode):

    attr = [('connection_mode', connection_mode)]
    controllers = self.db_get_val('Bridge', self.br_name, 'controller')
    controllers = ([controllers] if isinstance(controllers, uuid.UUID) else controllers)
    with self.ovsdb.transaction(check_error=True) as txn:
        for controller_uuid in controllers:
            txn.add(self.ovsdb.db_set('Controller', controller_uuid, *attr))
