[PATCH v3 8/8] doc: add missing headers to doxy-api-index.md

[Marat Khalili]

> I'm not sure we should add all in this index,
> especially the *_trace.h which are not really interesting.

These are all public headers, all of them have a man page and an HTML documentation page generated. Yet when a user clicks `API Reference` on dpdk.org they arrive here: https://doc.dpdk.org/api/ . Without listing all public headers this page is meaningless and misleading; web crawlers could also be confused by lack of direct access to inner pages.

I don't know specifics of *_trace.h pages, maybe they are special and should not be exposed. In this case we can add an exception, although I'd rather put them in a separate section explaining why they are special and not worth bothering with. After all users might be similarly puzzled.