Update git submodules

* Update docs/submodules/sdnvpn from branch 'stable/euphrates'
  - Fix defaultbranch in .gitreview

    Change-Id: Iffddd6ce6dedd50c74b673a5824b7f1bc1f459ea
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 21d4fce..685c549 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 21d4fcefd75f42c2939820982ac7c3daa9f97c4e
+Subproject commit 685c549bb39a1c1d538a1b8856ead0386f4aa08d