doc: update hairpin data buffer size config

  This patch updates the MLX5 PMD and release notes documentations.
Adding the guideline for hairpin data buffer size configuration.

Signed-off-by: Bing Zhao <bingz@mellanox.com>
---
 doc/guides/nics/mlx5.rst               | 11 +++++++++++
 doc/guides/rel_notes/release_20_05.rst |  1 +
 2 files changed, 12 insertions(+)
  

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Bing Zhao
> Sent: Thursday, April 9, 2020 6:51 PM
> To: john.mcnamara@intel.com; marko.kovacevic@intel.com; Slava Ovsiienko
> <viacheslavo@mellanox.com>; Matan Azrad <matan@mellanox.com>
> Cc: Shahaf Shuler <shahafs@mellanox.com>; Raslan Darawsheh
> <rasland@mellanox.com>; dev@dpdk.org
> Subject: [dpdk-dev] [PATCH] doc: update hairpin data buffer size config
> 
> This patch updates the MLX5 PMD and release notes documentations.
> Adding the guideline for hairpin data buffer size configuration.
> 
> Signed-off-by: Bing Zhao <bingz@mellanox.com>
> ---
>  doc/guides/nics/mlx5.rst               | 11 +++++++++++
>  doc/guides/rel_notes/release_20_05.rst |  1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
> index e13c07d..c3cde30 100644
> --- a/doc/guides/nics/mlx5.rst
> +++ b/doc/guides/nics/mlx5.rst
> @@ -99,6 +99,7 @@ Features
>  - Support for multiple rte_flow groups.
>  - Per packet no-inline hint flag to disable packet data copying into Tx
> descriptors.
>  - Hardware LRO.
> +- Hairpin.
> 
>  Limitations
>  -----------
> @@ -773,6 +774,16 @@ Run-time configuration
>    If this parameter is not specified, by default PMD will set
>    the smallest value supported by HW.
> 
> +- ``hp_buf_log_sz`` parameter [int]
> +
> +  The total data buffer size of a hairpin queue (logarithmic form), in bytes.
> +  PMD will set the data buffer size to 2 ** ``hp_buf_log_sz``, both for RX & TX.
> +  The capacity of the value is sepcified by the Firmware, and the initialization
> +  will get a failure if it is out of scope.
> +  A larger value is needed to support larger frame.
> +  If this parameter is not specified, by default PMD will set it to 16 and 9KB
> +  jumbo frames are supported.
> +

I think we need more clear  description what is the size range
and why not set to max or min.
In addition I think that the last line should be something like this:
By default PMD will set this value to 16, which mean that 9KB jumbo
frames will be supported.

>  .. _mlx5_firmware_config:
> 
>  Firmware configuration
> diff --git a/doc/guides/rel_notes/release_20_05.rst
> b/doc/guides/rel_notes/release_20_05.rst
> index 2596269..7128f26 100644
> --- a/doc/guides/rel_notes/release_20_05.rst
> +++ b/doc/guides/rel_notes/release_20_05.rst
> @@ -62,6 +62,7 @@ New Features
> 
>    * Added support for matching on IPv4 Time To Live and IPv6 Hop Limit.
>    * Added support for creating Relaxed Ordering Memory Regions.
> +  * Added support for configuring Haripin queue data buffer size.
> 
>  * **Updated the Intel ice driver.**
> 
> --
> 2.5.5