When the IP[46]Config changes, a new configuration gets assembled.
Before, whenever the new configuration was different than the current
one, the IP[46]Config of the device was completely replaced. This also
meant, that the old dbus IP[46]Config object was removed and the new one
was exported.
Now instead of recreating a new configuration, it updates the existing
(already exported) configuration in-place.
Also, add new gobject properties 'gateway' and 'searches' to the config class,
they will be exported over dbus.
Also, whenever any of the exported properties changes, make sure that a
notify signal gets emitted.
https://bugzilla.gnome.org/show_bug.cgi?id=707617
Signed-off-by: Thomas Haller <thaller@redhat.com>
