- drops nm_dispatcher_init(), which was called early in the main loop
  and created a proxy synchronously. Instead, the GDBusConnection is
  always ready.

- reuse the GDBusConnection of NMDBusManager. This means, we won't even
  try from in "initrd" configure-and-quit mode.

- as before, there is no "manager" instance. Instead, the data is stored
  in a global variable. That's ok. What is not OK is how the entire
  shutdown is handled (calling dispatcher blockingly, not waiting for
  requests to complete). That is fixable, but a lot of work. It is
  independent of whether we use a manager object or not.