Update git submodules

* Update docs/submodules/nfvbench from branch 'master'
  - [NFVBENCH-87] In case of asymmetric actual Tx rate, total drops is calculated incorrectly

    Use far end TX counter to calculate dropped packets at given RX port.

    Change-Id: Icfffb390e2e557f0bad2e9ddf685510decc25b27
    Signed-off-by: ahothan <ahothan@cisco.com>

diff --git a/docs/submodules/nfvbench b/docs/submodules/nfvbench
index e456fff..3918eba 160000 (submodule)
--- a/docs/submodules/nfvbench
+++ b/docs/submodules/nfvbench
@@ -1 +1 @@
-Subproject commit e456fff7801702f1cf672d9ebda54eabd5100ece
+Subproject commit 3918ebaca624bf6d58559d602eed8e33881e7ce0