Documentation: net/mlx5: Add blank line separator before numbered lists

The doc forgets to add separator before numbered lists, which causes the
lists to be appended to previous paragraph inline instead.

Add the missing separator.

Fixes: f2d51e57

 ("net/mlx5: Separate mlx5 driver documentation into multiple pages")
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>