[dpdk-dev] [RFC] net/mlx5: Descriptor status for Vectorized and MPRQ Rx

[Alexander Kozyrev]

There are two APIs that allow getting more insights about Rx queue operations:
- the rte_eth_rx_queue_count API gives the number of used descriptors.
- the rte_eth_rx_descriptor_status API provides the status of a Rx descriptor.
This information is available only for the regular Rx burst in the mlx5 driver.
The ENOTSUP value is returned for the Vectorized Rx burst or the MPRQ Rx burst.

Need to implement corresponding functions to compute the number of used
descriptors in an Rx queue for every Rx burst version available to DPDK users.
Once this is done we can check the required descriptor and tell whether it is
available for the hardware or being processed by the driver software.

Signed-off-by: Alexander Kozyrev <akozyrev at nvidia.com>