Allow registering rate object for devlink ports with dedicated
devlink_rate_leaf_{create|destroy}() API. Implement new netlink
DEVLINK_CMD_RATE_GET command that is used to retrieve rate object info.
Add new DEVLINK_CMD_RATE_{NEW|DEL} commands that are used for
notifications when creating/deleting leaf rate object.

Rate API is intended to be used for rate limiting of individual
devlink ports (leafs) and their aggregates (nodes).

Example:

$ devlink port show
pci/0000:03:00.0/0
pci/0000:03:00.0/1

$ devlink port function rate show
pci/0000:03:00.0/0: type leaf
pci/0000:03:00.0/1: type leaf
Co-developed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Dmytro Linkin <dlinkin@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>