BLE on ESP32 inconsistent init time (sometimes > 10s)

Initiating and activating bluetooth with
```python
import bluetooth
ble = bluetooth.BLE()
ble.active(True)
```
normally take around 200ms to execute. But sometimes it takes over 10 seconds.

occurs with `esp32-idf4-20191220-v1.12.bin`

Further Details at this [forum post](https://forum.micropython.org/viewtopic.php?f=18&t=7486).