net/mlx4: fix Tx packet drop application report

net/mlx4: fix Tx packet drop application report

When invalid lkey is sent to HW, HW sends an error notification in
completion function.

The previous code wouldn't crash but doesn't add any application report
in case of completion error, so application cannot know that packet
actually was dropped in case of invalid lkey.

Return back the lkey validation to Tx path.

Fixes: 2eee458746bc ("net/mlx4: remove error flows from Tx fast path")
Cc: stable@dpdk.org
Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>