Plugin broken, Homebridge is sent to infinit restart-loop
Latest version for Homebridge, Node.js, NPM.

```
Error: addMembership EADDRINUSE
    at Socket.addMembership (dgram.js:819:11)
    at /homebridge/node_modules/homebridge-shelly/node_modules/coap/lib/server.js:233:24
    at Array.forEach (<anonymous>)
    at Socket.<anonymous> (/homebridge/node_modules/homebridge-shelly/node_modules/coap/lib/server.js:232:42)
    at Socket.onListening (dgram.js:225:10)
    at Socket.emit (events.js:315:20)
    at startListening (dgram.js:150:10)
    at dgram.js:345:7
    at processTicksAndRejections (internal/process/task_queues.js:85:21)
    at runNextTicks (internal/process/task_queues.js:66:3)
```
