[Bug] SHDW2 does not stay registered
**Describe the bug**
SHDW2 does not stay registered, even though stale timeout is set to 0 or false
As this is a battery operated device, and is on a  door, sometimes it can be offline for days.
It keeps getting deregistered, and then when it comes backonline, it is in the Default Room and config has been lost.


**Log output**
Add any relevant parts from the homebridge log here, if applicable.
[02/01/2021, 17:18:00] [Shelly] Device SHDW-2 483FDA81F7F0 is stale. Unregistering its accessories.
[02/01/2021, 17:20:17] [Shelly] New device discovered: SHDW-2 483FDA81F7F0 at 192.168.0.196

**Environment:**
 - Shelly device(s): [e.g. Shelly 2.5] Shelly DoorWindow 2
 - Plugin version: [e.g. 0.14.0] homebridge-shelly v0.16.0
 - Device running homebridge: [e.g. Raspberry Pi]: raspberry pi
