libnm: unify property-to-dbus handling of NMSetting

Merge the function pointer get_func() into to_dbus_fcn().

Previously, get_func() as handled separately from to_dbus_fnc()
(formerly synth_func()). The notion was that synth-func would syntetize
properties that are D-Bus only. But that distinction does not seem
very helpful to me.

Instaed, we want to convert a property to D-Bus. Period. The
implementation should be handled uniformly. Hence, now that is
all done by property_to_dbus().

Note that property_to_dbus() is also called as default implementation
for compare-property. At least, for properties that are backed by a
GObject property.
11 jobs for <span class="ref-name">th/libnm-setting-cleanup</span> in 29 minutes and 34 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #261940
allowed to fail
checkpatch

00:01:03

passed #261947
t_debian:9

00:12:36

passed #261949
t_debian:sid

00:13:34

manual #261948
allowed to fail manual
t_debian:testing
passed #261941
t_fedora:28

00:21:51

passed #261942
t_fedora:29

00:29:34

passed #261943
t_fedora:30

00:22:07

manual #261944
allowed to fail manual
t_fedora:rawhide
passed #261945
t_ubuntu:16.04

00:13:53

passed #261946
t_ubuntu:18.04

00:12:45

 
  External
canceled NetworkManager test verification

00:00:04