Documentation: Add documentation for new devlink-rate attributes

``tx_max``

  Maximum TX rate value.

``tx_priority``

  Allows for usage of strict priority arbiter among siblings. This

  arbitration scheme attempts to schedule nodes based on their priority

  as long as the nodes remain within their bandwidth limit. The higher the

  priority the higher the probability that the node will get selected for

  scheduling.

``tx_weight``

  Allows for usage of Weighted Fair Queuing arbitration scheme among

  siblings. This arbitration scheme can be used simultaneously with the

  strict priority. As a node is configured with a higher rate it gets more

  BW relative to it's siblings. Values are relative like a percentage

  points, they basically tell how much BW should node take relative to

  it's siblings.

``parent``

  Parent node name. Parent node rate limits are considered as additional limits

  to all node children limits. ``tx_max`` is an upper limit for children.

  ``tx_share`` is a total bandwidth distributed among children.

``tx_priority`` and ``tx_weight`` can be used simultaneously. In that case

nodes with the same priority form a WFQ subgroup in the sibling group

and arbitration among them is based on assigned weights.

Arbitration flow from the high level:

#. Choose a node, or group of nodes with the highest priority that stays

   within the BW limit and are not blocked. Use ``tx_priority`` as a

   parameter for this arbitration.

#. If group of nodes have the same priority perform WFQ arbitration on

   that subgroup. Use ``tx_weight`` as a parameter for this arbitration.

#. Select the winner node, and continue arbitration flow among it's children,

   until leaf node is reached, and the winner is established.

#. If all the nodes from the highest priority sub-group are satisfied, or

   overused their assigned BW, move to the lower priority nodes.

Driver implementations are allowed to support both or either rate object types

and setting methods of their parameters.

and setting methods of their parameters. Additionally driver implementation

may export nodes/leafs and their child-parent relationships.

Terms and Definitions

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