net/mlx5: fix completion request for multi-segment

net/mlx5: fix completion request for multi-segment

The copying of sent mbufs pointers might be deferred to the end of
tx_burst() routine to be copied in one call of rte_memcpy.
For the multi segment packets this optimization is not applicable,
because number of packets does not match with number of mbufs and
we do not have linear array of pointers in pkts parameter.

The completion request generating routine wrongly took into account
the inconsistent (for multi-segment packets) deferred pointer copying.

Fixes: 5a93e173b874 ("net/mlx5: fix Tx completion request generation")

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>