It looks like in the `collect()` loop the `dsl_status` gauge is latched to 1 with the current status label set
```go
c.status.WithLabelValues(
c.host, c.identifier, status.DSLCfg.Status, status.DSLCfg.Modulation, status.DSLCfg.DataPath).Set(1)
```
However, this means that all historically seen statuses are latched to 1 and never reset to 0:
```
dsl_status{dataPath="",host="192.168.2.1",identifier="BT",modulation="",status="EstablishingLink"} 1
dsl_status{dataPath="",host="192.168.2.1",identifier="BT",modulation="",status="Initializing"} 1
dsl_status{dataPath="",host="192.168.2.1",identifier="BT",modulation="",status="NoSignal"} 1
```
Ideally in the `collect()` loop it would loop over all known status
values and set them to 0 for the ongoing publishes when the status has
changed. However, as a simpler workaround in this commit we just call
`.Reset()` on the gauge before the call to `.Set(1)` and that stops
publishing the metric label for the old statuses
