Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "trex_multistream: Add multistream support to T-Rex"
  - 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>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index e1080a5..518d5ba 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit e1080a507901f7b957f24c75170594b4f9bc9740
+Subproject commit 518d5bae6b5603b5b605830c690b0e91d0d26cd7