Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - xena_cont_bug_fix: Fix duration issue

    Port duration is in microseconds. I broke this with a previous
    commit.

    Change-Id: Id2770149355f40107ab8ee0523482b5867e0e72a
    Signed-off-by: Christian Trautman <ctrautma@redhat.com>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index e71e24e..8d528f2 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit e71e24ec001cfc06e27ce12c081ba749948b4599
+Subproject commit 8d528f2b4c66d94ea8760053f9bc75c595630056