Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "documentation: Installation prerequisites"
  - documentation: Installation prerequisites

    Added a mention of the default Python3 location used by virtualenv
    creation script after Python3 enforcement patch(/usr/bin/python3).
    Also added a paragraph warning of held-back kernel package version and
    DNF/APT/YUM configuration preventing modification of kernel packages.

    JIRA: MSP-10754

    Change-Id: I1ba630cf85af4d99cc2cbed40163a9137b95c390
    Signed-off-by: Richard Elias <richardx.elias@intel.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: Sridhar Rao <sridhar.rao@spirent.com>
    Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>
    Reviewed-by: Ian Stokes <ian.stokes@intel.com>