Update git submodules

* Update docs/submodules/sdnvpn from branch 'stable/danube'
  - Cleanup br-ex/br-quagga from testcase_3

    After the peering between Quagga and ODL within testcase 3
    cleanup br-ex (for fuel) or br-quagga (for apex) interfaces

    JIRA: SDNVPN-13

    Change-Id: I3e7bf91d4e47dfd7fe2a5068ed40ea4b2be48c6d
    Signed-off-by: tomsou <soth@intracom-telecom.com>
    (cherry picked from commit 0d8f3bf930bdd945d34188fb591a6deb03a999c5)

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 0a4bbb3..6b2a7d1 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 0a4bbb334ba31bccfab92d01deebb8e0ab4ccbfd
+Subproject commit 6b2a7d15d61e76da0bbaf5f60134119fd9b23cbe