_updateIcon should not attempt to sync any active connections, as the
icon-changed signal can be emitted in response to something done during
_syncActiveConnection. In the case of VPN, removeActiveConnection would
cause an icon-changed signal to be emitted immediately, but the state
would not be updated, causing us to call removeActiveConnection over and
over.

Explicitly sync all active connections when we know it needs to be done,
and simply make _updateIcon synchronize with the current device's icon.