net/mlx5: fix queue wrap-around of multi-packet send

net/mlx5: fix queue wrap-around of multi-packet send

When the WQ is wrapped around, it wrongly checks the condition when
resetting the pointer. It should be compared against the end of the queue,
not the beginning of the queue. And this isn't even needed when the length
of the copying data crosses the boundary.

Fixes: fdcb0f53053b ("net/mlx5: use work queue buffer as a raw buffer")
Cc: stable@dpdk.org
Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>