Update git submodules

* Update docs/submodules/sdnvpn from branch 'stable/danube'
  - Correct testcase 8 description

    jira: SDNVPN-138

    Change-Id: If56b58b003ce2e024883a015a964e3ff3ded53f5
    Signed-off-by: Nikolas Hermanns <nikolas.hermanns@ericsson.com>
    (cherry picked from commit 9a52d17d9ac79c358647d87b5d540e869b25769d)

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 3be7276..5c28dc1 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 3be72766b6686072d1014a4b3bac56c373a5ed6a
+Subproject commit 5c28dc19e72ffbbaf652ff6b5c48d7fe72bdd9c4