rpi2-daq/usr/bin/btrn default auth mode

The usage message for btrn says the default authorization mode is set to 0, no auth.
When configuring the radio, however, it does:

```python
if cfg['Profile'] != 'SPP':
                # print("setting profile=SPP")
                cmd = 'S~,0'
                send_command(pexp, cmd)
```

So its always set to SPP.  I think the usage message needs to be changed.
