BLEAdvertisedDevice getPayload() how do I get total_len of payload

I want raw payload to parse it myself.
I found there is no total_len in BLEAdvertisedDevice

```
class MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks {
  void onResult(BLEAdvertisedDevice advertisedDevice) {
    uint8_t *payload = advertisedDevice.getPayload();
    // I can't get total_len so I can't loop,
    // or may be I should limit total_len to 62?
  }
}
```

