maintainers: resign from mlx4 maintenance
maintainers: resign from mlx4 maintenance

I have been a little too busy these past months and could not follow all
the re-work of this PMD.

So the best thing for this PMD would be to move the mlx4 maintenance to
more involved people.

Cc: stable@dpdk.org

Signed-off-by: Nelio Laranjeiro <2f8dd9032d5b85ca4b53dec8ce664eb6998836be@6wind.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk