Documentation: net/mlx5: Wrap vnic reporter devlink commands in code blocks

Sphinx reports htmldocs warnings:

Documentation/networking/device_drivers/ethernet/mellanox/mlx5/devlink.rst:287: WARNING: Unexpected indentation.
Documentation/networking/device_drivers/ethernet/mellanox/mlx5/devlink.rst:288: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/networking/device_drivers/ethernet/mellanox/mlx5/devlink.rst:290: WARNING: Unexpected indentation.

Fix above warnings by wrapping diagnostic devlink commands in "vnic
reporter" section in code blocks to be consistent with other devlink
command snippets.

Fixes: b0bc615d ("net/mlx5: Add vnic devlink health reporter to PFs/VFs")
Fixes: cf14af14 ("net/mlx5e: Add vnic devlink health reporter to representors")
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>

Documentation/networking/device_drivers/ethernet/mellanox/mlx5/devlink.rst

@@ -283,10 +283,14 @@ nic_receive_steering_discard: number of packets that completed RX flow
 steering but were discarded due to a mismatch in flow table.
 
 User commands examples:
-- Diagnose PF/VF vnic counters
+
+- Diagnose PF/VF vnic counters::
+
         $ devlink health diagnose pci/0000:82:00.1 reporter vnic
+
 - Diagnose representor vnic counters (performed by supplying devlink port of the
-  representor, which can be obtained via devlink port command)
+  representor, which can be obtained via devlink port command)::
+
         $ devlink health diagnose pci/0000:82:00.1/65537 reporter vnic
 
 NOTE: This command can run over all interfaces such as PF/VF and representor ports.