net/mlx5: fix Tx queue size created with DevX

net/mlx5: fix Tx queue size created with DevX

The number of descriptors specified for queue creation
implies the queue should be able to contain the specified
amount of packets being sent. Typically one packet takes
one queue descriptor (WQE) to be handled. If there is inline
data option enabled one packet might require more WQEs to
embrace the inline data and the overall queue size (the
number of queue descriptors) should be adjusted accordingly.

In mlx5 PMD the queues can be created either via Verbs, using
the rdma-core library or via DevX as direct kernel/firmware call.
The rdma-core does queue size adjustment internally, depending on
TSO and inline setting. The DevX approach missed this point.
This caused the queue size discrepancy and performance variations.

The patch adjusts the Tx queue size for the DevX approach
in the same as it is done in rdma-core implementation.

Fixes: 86d259cec852 ("net/mlx5: separate Tx queue object creations")
Cc: stable@dpdk.org
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>