ethdev: add traffic management ops get API

ethdev: add traffic management ops get API

The rte_flow feature breaks the monolithic approach for ethdev by
introducing the new rte_flow API to ethdev using a plugin-like approach.

Basically, the rte_flow API is still logically part of ethdev:
- It extends the ethdev functionality: rte_flow is a new feature/
  capability of ethdev;
- all its functions work on an Ethernet device: the first parameter of the
  rte_flow functions is Ethernet device port ID.

Also, the rte_flow API is a sort of capability plugin for ethdev:
- the rte_flow API functions have their own name space: they are called
  rte_flow_operationXYZ() as opposed to rte_eth_dev_flow_operationXYZ());
- the rte_flow API functions are placed in separate files in the same
  librte_ether folder as opposed to rte_ethdev.[hc].

The way it works is by using the existing ethdev API function
rte_eth_dev_filter_ctrl() to query the current Ethernet device port ID for
the support of the rte_flow capability and return the pointer to the
rte_flow operations when supported and NULL otherwise:

struct rte_flow_ops *eth_flow_ops;
int rte = rte_eth_dev_filter_ctrl(eth_port_id,
	RTE_ETH_FILTER_GENERIC, RTE_ETH_FILTER_GET, &eth_flow_ops);

This patch reuses the same approach for ethdev Traffic Management API.

Signed-off-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>
Acked-by: Keith Wiles <keith.wiles@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>