Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "xena_pairs: Add pairs topology for 2544 testing"
  - xena_pairs: Add pairs topology for 2544 testing

    Add xena pairs topology and port removal options for JSON
    files with RFC2544 testing.  Refactored JSON code for
    better expansion later.

    Resolved pathing issues related to previous patch allowing
    for execution of VSPerf from any directory.

    JIRA: VSPERF-502

    Change-Id: Ida60c1223ae0f45f8879351770ab7fdce859b59b
    Signed-off-by: Christian Trautman <ctrautma@redhat.com>