Update git submodules

* Update docs/submodules/nfvbench from branch 'master'
  - Update doc/faq and config comments

    Change-Id: I263f2d33ef9010d4ead0a26c390736a11edaaa20
    Signed-off-by: ahothan <ahothan@cisco.com>

diff --git a/docs/submodules/nfvbench b/docs/submodules/nfvbench
index 0ab04ab..3154998 160000 (submodule)
--- a/docs/submodules/nfvbench
+++ b/docs/submodules/nfvbench
@@ -1 +1 @@
-Subproject commit 0ab04ab7103fc4bfb17042b60c1e005049375cc2
+Subproject commit 31549982d3bb674ee251cc3f1e9f358badbf632d