Configuration options can be changed at runtime

[MarcinMiklas]

This will allow creating GUI for openavb_harness.

Example use cases.

To change volume at runtime enter in openavb_harness:

c0 intf_nv_volume -20

To change filename of played wav file:

c1 intf_nv_file_name test2.wav

c0, c1 means stream 0, stream 1 respectively.

Of course, it is not particularly handy to enter whose commands manually, but you can write the GUI wrapper which runs the openavb_harness and then issues those commands in response to user actions.

[andrew-elder]

This looks ok to me. Any other comments?

[bdthomsen]

It looks OK to me as well, though I would have appreciated some comments describing what the new functions do.