Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "trex_learning: Add learning packet option to T-Rex testing"
  - trex_learning: Add learning packet option to T-Rex testing

    Adds packet learning option which is available on other
    Traffic generators as a feature. This adds this feature to the
    Trex implementation inside of VSPerf.

    JIRA: VSPERF-547

    Change-Id: Iaf4d0721b22eb780c25e29295c112d4fcb47b22c
    Signed-off-by: Christian Trautman <ctrautma@redhat.com>