This can be set to 'preserve', 'permanent', 'random' or 'stable'. We
need to handle these values otherwise we can end up with the editor
being un-saveable.
Turn the entry in to a GtkComboBoxText with those items in it, allowing
a mac address to be typed too.
Partial copy of 85b6b659a140a59c3df787062e089a0b4e2a547d from
network-manager-applet.
We also remove support for WiMAX (now unsupported by NetworkManager),
and InfiniBand (Enterprise feature), and the use of
the deprecated NM_SETTING_WIRELESS_SEC property.
With help from network-manager-applet patches by Jiří Klimeš and
Dan Winship.
https://bugzilla.gnome.org/show_bug.cgi?id=765910
