Update git submodules

* Update docs/submodules/nfvbench from branch 'stable/euphrates'
  - 5.1.0 release notes

    Change-Id: I4937f7c6155eb7dbe8e7c4cc5b3a4ff3e043f374
    Signed-off-by: ahothan <ahothan@cisco.com>

diff --git a/docs/submodules/nfvbench b/docs/submodules/nfvbench
index 1a69436..cf9c95c 160000 (submodule)
--- a/docs/submodules/nfvbench
+++ b/docs/submodules/nfvbench
@@ -1 +1 @@
-Subproject commit 1a694362729de72c9703719d587abcb96f0f3f0a
+Subproject commit cf9c95ccda2f5afbdf79c7debe5fcd88c05eaa6a