ipfs daemon --offline returns 400 for /api/v0/stats/bw

If your run

```console
ipfs daemon --offline
```
then the API responds to requests for `/api/v0/stats/bw` with a `400` status code and the body:

```json
{"Message":"this command must be run in online mode. Try running 'ipfs daemon' first","Code":1,"Type":"error"}
```

as we're using the bandwidth stats to determine if the connection is working, the Web UI asserts that the connection to IPFS has failed.