[DPM] DO can start network logging and listen for events

This CL adds:
1) Setter and getter in DPM to manipulate logging switch (retrieval
method to come in a subsequent CL(s)).
2) A way for DPM to register to listen for events.
3) Skeleton of NetworkLogger class (more to come in subsequent CL(s)).

Bug: 29748723
Change-Id: I5c04662ccc6febd2ba294b0eaca1ed1da9c16e47