{IB, net}/mlx5: E-Switch, Use index of rep for vport to IB port mapping

In the single IB device mode, the mapping between vport number and
rep relies on a counter. However for dynamic vport allocation, it is
desired to keep consistent map of eswitch vport and IB port.

Hence, simplify code to remove the free running counter and instead
use the available vport index during load/unload sequence from the
eswitch.

Signed-off-by: Bodong Wang <bodong@mellanox.com>
Suggested-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>