net/mlx5: Use devl_ API for rate nodes destroy

Use devl_rate_nodes_destroy() instead of devlink_rate_nodes_destroy().
Add devlink instance lock in the driver paths to this function to have
it locked while calling devl_ API function.

This will be used by the downstream patch to invoke
mlx5_devlink_eswitch_mode_set() with devlink lock held.

Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>