Update git submodules

* Update docs/submodules/sdnvpn from branch 'stable/danube'
  - Reduce overview

    Change-Id: Ifb8915d62ea26f44f29c4d3b84beecd78dceae9e
    Signed-off-by: Nikolas Hermanns <nikolas.hermanns@ericsson.com>
    (cherry picked from commit c063e49cec6afa6ba1ab743a86482768fe1cc28e)

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 2bec15d..27f6523 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 2bec15d7d92172681771fd4567b959662087d7b7
+Subproject commit 27f6523b80923324c00360abbd2bb85d99c0f86e