Update git submodules

Update git submodules

* Update docs/submodules/sdnvpn from branch 'stable/euphrates'
  - comment multiple subnet configuration

    * commenting multiple subnet configuration under a neutron network because ODL
    doesn't have a support for it yet (netvirt bug: https://bugs.opendaylight.org/show_bug.cgi?id=9239)
    * This has to be uncommented once the above bug is fixed.

    Change-Id: I4c863fbdd951891035471f1a10cf18546f5218e0
    Signed-off-by: Periyasamy Palanisamy <periyasamy.palanisamy@ericsson.com>
    (cherry picked from commit b0c56bc3276a25df4e387ee08734ad292487cf8e)