Add support for all-stations or broadcast messages

[atmurray]

Have started a proof of concept here:
https://github.com/atmurray/dnp3/compare/broadcast

Main challenge seems to be how to signal to upper/application layer that IIN1.0 needs to be set and when it should be cleared. Not sure if some of the work being undertaken in the addressrefactor branch is to pave the way for this?

[jadamcrain]

Yes. The goal of the addressrefactor branch is to add support for broadcast, self-address, and allowing outstation to respond to any master (optionally).

This is the only remaining conformance item for Level 2 based on testing with the ASE 2000.

The link addresses have to be pushed up through the transport re-assembly and then to the app layer.

[jadamcrain]

Some work has been done to get the link-layer addresses up into the application layer to make this possible, and we're going to do this in 3.0.0.