net/mlx5: Fix lag port remapping logic

Fix the logic so that if both ports netdevices are enabled or disabled,
use the trivial mapping without swapping.

If only one of the netdevice's tx is enabled, use it to remap traffic to
that port.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>