Request for api to set alc sync periodicity

Would e great if there was a way to set the periodicity of alc sync, today it appears fixed in lorawan_alcsync_v2.0.0.c

```
#define ALC_SYNC_DEFAULT_REQUEST_PERIOD_S ( 129600UL )  // 36 hours
```

and there aren't any accessors to set this field.

Would be great to be able to pull this in a bit and sync at arbitrary time intervals.