Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Uplifting docs to D-2

    Change-Id: I8824d0620be1fff1786ed401c78062e96ca7df52
    Signed-off-by: Nikolas Hermanns <nikolas.hermanns@ericsson.com>

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 88331de..19ff281 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 88331de3fb9375d316acba7b160ddf2a9beab5b2
+Subproject commit 19ff2816a46f1c4828ea104bbe0361e2d5b93ba5