NetworkHandler: make status callback private, reorder functions #16

The status callback function now gets privately declared at the earliest
possible moment, to both allow for reordering of code and avoid calling
this function directly from any other part of the code

• void changed to static void in status_callback declaration
• this now makes it possible to define network_init before
  status_callback, as status_callback is declared much earlier

NetworkHandler: make status callback private, reorder functions

Nice! Thanks.