Port loopback commands

configure
    - system
        - loopback-no-svc-port [mac-swap mac-swap port-id] [mirror mirror-port-id] [testhead testhead port-id] [p2mpbud p2mpbud-port-id [p2mp-bud-classification]]
        - no loopback-no-svc-port [mac-swap mac-swap port-id] [mirror mirror-port-id] [testhead testhead port-id] [p2mpbud p2mpbud-port-id]