RDMA/mlx5: Free second uplink ib port

The cited patch introduce ib port for the slave device uplink in
case of multiport eswitch. However, this ib port didn't perform
anything when unloaded.
Unload the new ib port properly.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>