code: func RequestRXTimingSetup(del int) storage.MACCommandBlock {
  	return storage.MACCommandBlock{
  		CID: lorawan.RXTimingSetupReq,
  		MACCommands: []lorawan.MACCommand{
  			{
  				CID: lorawan.RXTimingSetupReq,
  				Payload: &lorawan.RXTimingSetupReqPayload{
  					Delay: uint8(del),
  				},
  			},
  		},
  	}
  }
docs: // RequestRXTimingSetup modifies the RX delay between the end of the TX
  // and the opening of the first reception slot.