Update git submodules

* Update docs/submodules/vswitchperf from branch 'stable/euphrates'
  - trex_multistream: Add multistream support to T-Rex

    Adds incremental source multi-stream functionality to
    T-Rex traffic generator code in VSPerf.

    JIRA: VSPERF-532

    Change-Id: Ib5ba326699d89350ac1715c9a4276e5fa46a133e
    Signed-off-by: Christian Trautman <ctrautma@redhat.com>
    (cherry picked from commit d4054052bdc6d9417e27f81f2434bcf1f2149972)

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index 55429d9..d126de9 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit 55429d9203032fe7b5dd9ac81cec81cec4e4a17d
+Subproject commit d126de94bea2e5d0e237dc6a3373fd3d53e3cfa3