Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "trex: Tests with T-Rex in VM"
  - trex: Tests with T-Rex in VM

    Patch introduces a set of testcases with T-Rex running inside VM.

    JIRA: VSPERF-560

    Change-Id: I5b0a0220a2d72428ae1210ee9590d39abdfb9c1d
    Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
    Signed-off-by: RadoslawX Glombiowski <radoslawx.glombiowski@intel.com>
    Reviewed-by: Al Morton <acmorton@att.com>
    Reviewed-by: Christian Trautman <ctrautma@redhat.com>
    Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>