Update git submodules

* Update docs/submodules/vswitchperf from branch 'stable/danube'
  - Added index files user and developer docs

    Change-Id: I37b8acb98bca6fa4428be2722496eb1f7a476798
    Signed-off-by: Trevor Cooper <trevor.cooper@intel.com>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index 5abdc22..1e00995 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit 5abdc227fb523669250c046f1b28d86004693f58
+Subproject commit 1e00995886720000624145ad181ea70ac97a233a