Following the previous commit, this patch adapts the
NetDeviceSimple layout to be consistent with the other
devices in the Network panel.
This is, however, a temporary solution, for simple devices
will be handled in a separate panel in the future.
https://bugzilla.gnome.org/show_bug.cgi?id=786662
Rename NetDeviceWired to NetDeviceEthernet, but split out most of the
code into a new NetDeviceSimple superclass that can later be used for
other device types that we provide only minimal UI/support for.
https://bugzilla.gnome.org/show_bug.cgi?id=677143