Update git submodules

* Update docs/submodules/sdnvpn from branch 'master'
  - Use Neutron API for attaching floating ip address

    The Nova API for attaching floating ip address with vm instance is
    removed in latest Openstack release. Hence moving to neutron API for
    attaching floating ip address with VM.

    JIRA: SDNVPN-217

    Change-Id: If321191eca0915cfd816eabc8890b28ed79cefc7
    Signed-off-by: Periyasamy Palanisamy <periyasamy.palanisamy@ericsson.com>

diff --git a/docs/submodules/sdnvpn b/docs/submodules/sdnvpn
index 3355eda..c4ac6f6 160000 (submodule)
--- a/docs/submodules/sdnvpn
+++ b/docs/submodules/sdnvpn
@@ -1 +1 @@
-Subproject commit 3355eda6176c0a78b77143c9735c9a5c2a61d525
+Subproject commit c4ac6f6475fe7a6b7ebceba1a7af3ee6af5138fe