net/mlx5: Add support for setting tc-bw on nodes

net/mlx5: Add support for setting tc-bw on nodes

Introduce support for enabling and disabling Traffic Class (TC)
arbitration for existing devlink rate nodes. This patch adds support
for a new scheduling node type, `SCHED_NODE_TYPE_TC_ARBITER_TSAR`.

Key changes include:

- New helper functions for transitioning existing rate nodes to TC
  arbiter nodes and vice versa. These functions handle the allocation
  of TC arbiter nodes, copying of child nodes, and restoring vport QoS
  settings when TC arbitration is disabled.

- Implementation of `mlx5_esw_devlink_rate_node_tc_bw_set()` to manage
  tc-bw configuration on nodes.

- Introduced stubs for `esw_qos_tc_arbiter_scheduling_setup()` and
  `esw_qos_tc_arbiter_scheduling_teardown()`, which will be extended in
  future patches to provide full support for tc-bw on devlink rate
  objects.

- Validation functions for tc-bw settings, allowing graceful handling
  of unsupported traffic class bandwidth configurations.

- Updated `__esw_qos_alloc_node()` to insert the new node into the
  parent’s children list only if the parent is not NULL. For the root
  TSAR, the new node is inserted directly after the allocation call.

- Don't allow `tc-bw` configuration for nodes containing non-leaf
  children.

This patch lays the groundwork for future support for configuring tc-bw
on devlink rate nodes. Although the infrastructure is in place, full
support for tc-bw is not yet implemented; attempts to set tc-bw on
nodes will return `-EOPNOTSUPP`.

No functional changes are introduced at this stage.

Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Link: https://patch.msgid.link/20250629142138.361537-6-mbloch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>