Update git submodules

* Update docs/submodules/nfvbench from branch 'master'
  - Move to tag 1.2.6 and nfvbenchvm 0.6

    Change-Id: Ib38e033baca0145db3cc940ca92c5ba73d5717e7
    Signed-off-by: Yichen Wang <yicwang@cisco.com>

diff --git a/docs/submodules/nfvbench b/docs/submodules/nfvbench
index 5436500..0843235 160000 (submodule)
--- a/docs/submodules/nfvbench
+++ b/docs/submodules/nfvbench
@@ -1 +1 @@
-Subproject commit 54365002e932743f693af28d3f568c20a9e18513
+Subproject commit 0843235ecbb375d1d759a67791348e7812851029