docs: def _init_dut(self):
          """Initialize the DUT.
  
          DUT will be restarted. and openthread will started.
          """
          if self.auto_dut:
              self.dut = None
              return
  
          dut_port = settings.DUT_DEVICE[0]
          dut = OpenThreadController(dut_port)
          self.dut = dut