net/mlx4: revert fast verbs interface for Tx

net/mlx4: revert fast verbs interface for Tx

This reverts commit 9980f81dc2623291b89cf1c281a6a9f116fd2394.

"Fast Verbs" is a nonstandard experimental interface that must be reverted
for compatibility reasons. Its replacement is slower but temporary,
performance will be restored by a subsequent commit through an enhanced
data path implementation. This one focuses on maintaining basic
functionality in the meantime.

Signed-off-by: Moti Haimovsky <motih@mellanox.com>
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>