[dpdk-dev] [RFC] net/mlx5: add metering support

[Suanming Mou <suanmingm@mellanox.com>]

The mlx5 PMD will support the rte_mtr APIs with type srTCM(IETF RFC 
2697) color blind mode.

The metering flow will be composed of three flow tables, the prefix 
table, the metering table and the suffix table.
         packet ----> prefix table ----> metering table ----> suffix table

The prefix table and suffix table divide the user defined flow actions 
as some of the actions only make sense after the metering and some need 
before the metering(mainly for the *_DECAP actions).
The metering table validates the packet should pass or not and can be 
updated independently once the metering policy updating comes.

The register with unique flow id for the packet will be used to match 
the prefix and suffix flow tables for one flow in case messing up with 
other flows sharing the same metering rule.
The color of the packet also uses register match but will be the 
different register.

For the prefix table, mainly two actions, reformat action set the unique 
flow id, metering action generate the color.
         packet ----> pattern match ----> user defined actions apply 
----> set unique id ----> set color ----> metering table

For the metering table, validate the color with the configured policy, 
send to the next table or dropped.
         packet ----> color match(drop not matched packet) ----> suffix 
table

For the suffix table, apply the left actions if the id matches the 
prefix table reformat action has been set.
         packet ----> id match ----> user defined actions apply

The APIs will be supported:
rte_mtr_capabilities_get
rte_mtr_meter_profile_add
rte_mtr_meter_profile_delete
rte_mtr_create
rte_mtr_destroy
rte_mtr_meter_disable
rte_mtr_meter_enable
rte_mtr_meter_profile_update
rte_mtr_stats_update
rte_mtr_stats_read

The APIs will not be supported:
rte_mtr_meter_dscp_table_update
rte_mtr_policer_actions_update