Update git submodules

Update git submodules

* Update docs/submodules/samplevnf from branch 'master'
  - Merge "Fix using signature in latency measurements"
  - Fix using signature in latency measurements

    When doing latency measurements the generator can add a
    32 bits signature in the packet at a specific location,
    so that the receiver only uses the packets generated by the
    generator and ignores packets generated for instance by a switch
    The is particuly important for latency measurements as we use
    data in the packets as timestamps, and packets generated elsewhere
    would result in random latency for those packets.

    Change-Id: I8352b35aff76ec8d1344a1e492b9dcc20a53f1ce
    Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>