Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "trex: Add support Trex traffic generator"
  - trex: Add support Trex traffic generator

    Topology are two physical servers, on first is trex and second is VSPERF.
    Trex is running in stateless mode this means that on server where is located
    trex repo is running trex binary file and VSPERF working with server via
    python API.

    JIRA: VSPERF-528

    Change-Id: Id8819495325ebc13fdce365f4af0e040ce68cd0e
    Signed-off-by: Martin Goldammer <martin.goldammer6@gmail.com>
    Reviewed-by: Martin Klozik <martinx.klozik@intel.com>
    Reviewed-by: Al Morton <acmorton@att.com>
    Reviewed-by: Christian Trautman <ctrautma@redhat.com>
    Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>