Update git submodules

* Update docs/submodules/nfvbench from branch 'master'
  - Updated docker tag

    Change-Id: If7b1d56d099bf8aae374baff91e8ab41572d4311
    Signed-off-by: Kerim Gokarslan <kgokarsl@cisco.com>

diff --git a/docs/submodules/nfvbench b/docs/submodules/nfvbench
index 34cbe70..2162332 160000 (submodule)
--- a/docs/submodules/nfvbench
+++ b/docs/submodules/nfvbench
@@ -1 +1 @@
-Subproject commit 34cbe7031415297ee5c2b6c7059801603398fa7f
+Subproject commit 216233299e082d2f3a67a697be66bb894f23f011