Update git submodules

* Update docs/submodules/samplevnf from branch 'master'
  - Added developer user guide draft for samplevnfs

    Change-Id: I15a5f7ae8e3aac5d509b7a722f7032fbd2da69d0
    Signed-off-by: Deepak S <deepak.s@linux.intel.com>

diff --git a/docs/submodules/samplevnf b/docs/submodules/samplevnf
index ada9512..4a31f76 160000 (submodule)
--- a/docs/submodules/samplevnf
+++ b/docs/submodules/samplevnf
@@ -1 +1 @@
-Subproject commit ada951272b7d7cc06dd0086276586d1d4032261d
+Subproject commit 4a31f76b5f3e1caad12b7cc3bfe97ee1f0dacfc7