Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "docs: Update step driven test documentation"
  - docs: Update step driven test documentation

    A minor update of step driven documentation, which should help
    with better understanding of this feature.

    Change-Id: I58d1483f98520a008c8cbea9c820343c33835e6f
    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>