enter arbitrary mode

def set_mode_px4(self, mode, custom_mode, custom_sub_mode):
        '''enter arbitrary mode'''
        if isinstance(mode, str):
            mode_map = self.mode_mapping()
            if mode_map is None or mode not in mode_map:
                print("Unknown mode '%s'" % mode)
                return
            # PX4 uses two fields to define modes
            mode, custom_mode, custom_sub_mode = px4_map[mode]
        self.mav.command_long_send(self.target_system, self.target_component,
                                   mavlink.MAV_CMD_DO_SET_MODE, 0, mode, custom_mode, custom_sub_mode, 0, 0, 0, 0)