Update git submodules

* Update docs/submodules/releng from branch 'master'
  - create stable/fraser branch for sdnvpn

    Change-Id: Ibe0e92b2b3772c53df66e10bf7059be4754d4646
    Signed-off-by: Periyasamy Palanisamy <periyasamy.palanisamy@ericsson.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index bd72451..51912fe 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit bd72451d3b714b95789f6128f9d0cf7d82514fa6
+Subproject commit 51912fece5edcf019a4ff551d54619c42fcea91d