[PATCH v2] doc: add flex item API examples

[Thomas Monjalon]

21/11/2021 09:18, Gregory Etelson:
> Demonstrate flex item API usage on known network protocols.
> 
> Signed-off-by: Gregory Etelson <getelson at nvidia.com>
> Reviewed-by: Viacheslav Ovsiienko <viacheslavo at nvidia.com>
> ---
>  doc/guides/howto/flex_item.rst | 618 +++++++++++++++++++++++++++++++++

There's a lot of code in this doc,
it would be better to have it in an example app and integrate it in the doc
with the syntax literalinclude suggested in doc/guides/contributing/documentation.rst

Also this is all about rte_flow so it should fit
in the existing doc doc/guides/howto/rte_flow.rst