Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - vpp: Define vppctl socket name

    Newer versions of VPP require an explicit definition of CLI socket
    file for proper functionality. Otherwise vppctl is not able to connect
    to running vpp process and thus vsperf is not able to configure
    and control vpp.

    Change-Id: Id0df75fd0894e22b1b4d7fa05e16f49efe20d3ab
    Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
    Reviewed-by: Al Morton <acmorton@att.com>
    Reviewed-by: Christian Trautman <ctrautma@redhat.com>
    Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
    Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>