[v2] doc: disable doxygen's HAVE_DOT tag

  Ubuntu ships with a patched version of doxygen that enables
HAVE_DOT (disabled by default). Enabling this option causes the warning:
"""
warning: Included by graph for 'rte_common.h' not generated,
too many nodes. Consider increasing DOT_GRAPH_MAX_NODES
"""
This reproduces with doxygen version 1.8.13 and
dot - graphviz version 2.40.1 on Ubuntu 18.04.

This will force doxygen not to assume that dot (part of Graphviz)
is installed, and will result in dot not being used for visualization.

If someone still needs to generate the graphs, the following can
be considered:
- Increase DOT_GRAPH_MAX_NODES to a large value.
- Set HAVE_DOT for more powerful graphs.
- Set DOT_IMAGE_FORMAT=svg to generate svg images.
- Set INTERACTIVE_SVG=YES to allow zooming and panning.

See:
- http://changelogs.ubuntu.com/changelogs/pool/main/d/doxygen/doxygen_1.8.13-10/changelog
- http://www.doxygen.nl/manual/config.html#cfg_have_dot
- https://github.com/doxygen/doxygen/issues/7345

Signed-off-by: Ali Alnubani <alialnu@mellanox.com>
---
 doc/api/doxy-api.conf.in | 2 ++
 1 file changed, 2 insertions(+)

Changes in v2:
- Updated commit's body.
  

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Ali Alnubani
> Sent: Wednesday, October 23, 2019 12:56 PM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH v2] doc: disable doxygen's HAVE_DOT tag
> 
> Ubuntu ships with a patched version of doxygen that enables HAVE_DOT
> (disabled by default). Enabling this option causes the warning:


We have also started seeing this on some recent build systems as well.
Thanks for the fix. I think this should be merged soon in case it break
doc builds for other people.


Acked-by: John McNamara <john.mcnamara@intel.com>
  

> > Ubuntu ships with a patched version of doxygen that enables HAVE_DOT
> > (disabled by default). Enabling this option causes the warning:
> 
> 
> We have also started seeing this on some recent build systems as well.
> Thanks for the fix. I think this should be merged soon in case it break
> doc builds for other people.
> 
> 
> Acked-by: John McNamara <john.mcnamara@intel.com>

Applied, thanks