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.
This code is fairly independent of the rest, and we don't want
net-device-wifi.c to become too massive and unmaintainable.
The code in connection-editor/ is fairly similar to
nm-connection-editor, with some simplification because we
currently only edit wireless connections.
The code in wireless-security/ is almost a straight copy
of the same code in nm-connection-editor, with some changes
to the .ui files to make them fit better in the new design.
