Update git submodules

Update git submodules

* Update docs/submodules/samplevnf from branch 'master'
  - Get multiple port stats simultaneously

    JIRA: YARDSTICK-1220

    Implemented new "multi port stats <port list>" command, which returns a
    semi-colon-separated list of comma-separated values:
    - port id
    - total (at last_tsc) for rx_pkts, tx_pkts, no_mbufs, ierrors + imissed
    - last_tsc

    Change-Id: I8a8da79cb4ccb245ccb38b50b561da51a40a359d
    Signed-off-by: Patrice Buriez <patrice.buriez@intel.com>