[cmaster-next] support for capnproto API on Quagga

[Philippe Guibert]

Hi all,

I am working on some support of capnproto interface on Quagga
(following David's contribution).
In order to avoid duplication of effort, I would like first to get
your review from cmaster-next community,
The code can be seen here:

https://lists.quagga.net/pipermail/quagga-dev/2016-December/016521.html

then, based on your reviews, I'll update the patch series and I'll
work to rebase it on cmaster-next too.

Thanks,

Regards,

Philippe