Change the default status of quality of service back to disabled,
as it hurts performance in some cases.

Fixes: 38438f7c ("net/mlx4: Set enhanced QoS support by default when ...")
Signed-off-by: NMoshe Lazer <moshel@mellanox.com>
Signed-off-by: NTariq Toukan <tariqt@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>