Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - trex: Add support for traffic capture

    A support of traffic capture was added into T-Rex.
    It allows to write a functional tests, which will
    verify proper vSwitch functionality by inspection
    of packets received by T-Rex.
    A testcase example was added into integration
    testcases.

    JIRA: VSPERF-556

    Change-Id: I5ad28479ca2ec29760b68f24510af1a6d74866ae
    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>
    Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>
    Reviewed-by: Richard Elias <richardx.elias@intel.com>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index a2d97b0..ce8e18d 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit a2d97b05fb3b7ff62f62bcb16d36c51e3df6ca77
+Subproject commit ce8e18ddcfb84f887aa91f38133781da2f592309