Hide "no internet connection" when connected some other way.

We now track whether the device is connected at all, and use
this to suppress the disconnected message in the mobile
status string (we previously just looked at wifi
connectivity).

So, if a device is attached via ethernet:

- On wifi-only devices, the combined label is shown in the
  notification panel, so you'll see "ETHERNET" (this comes
  straight from EthernetDataTracker; at some point we need
  localized strings and icons).

- On mobile-data devices (phones), the notification panel
  only shows the mobile data label, which will be
  suppressed, so you'll see nothing at all.

Bug: 6648292
Change-Id: I9841eaeffe50a4f046afbdc09d80c5bd4d78a839