[Reviewer: Andy] Stress fixes

Andy, please can you take a quick look over the sprout fixes coming out of my stress runs last sprint.  The commits are pretty self-explanatory:

- Take latest pjsip-upstream (incorporating a fix Mike has already reviewed and merged to master)
- Match per-bono load with that specified in deployment sizing spreadsheet
- Reimplement cw_stat in C++ to make it blazingly fast