net/mlx5: fix legacy multi-packet write session

net/mlx5: fix legacy multi-packet write session

To provide the better PCIe bandwidth utilization the ConnectX-4LX
NIC supports the multi-packet write (MPW) sessions allowing to
pack multiple packets into one descriptor (WQE). This is legacy
feature and it has some limitations on the packets and data
description segments. To provide the best performance all inline
packets must be put into shared data segment and the total length
of MPW session must be limited. The limit is controlled with
txq_inline_mpw devarg.

Fixes: 82e75f8323bf ("net/mlx5: fix legacy multi-packet Tx descriptors")
Cc: stable@dpdk.org
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>