net/mlx5: Preserve rate settings when creating a rate node

Modify `esw_qos_create_node_sched_elem()` to receive max_rate and
bw_share values while maintaining the previous configuration.

This change is essential for the upcoming patch that will modify rate
nodes and requires the existing settings to be preserved unless
explicitly changed.

Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1741642016-44918-4-git-send-email-tariqt@nvidia.com


Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>