Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "BugFix: Negative dropped packets in Prox tests"
  - BugFix: Negative dropped packets in Prox tests

    Removed the abs function which can potentially mask
    negative dropped packets.

    Dropped packets in Prox workload VNF = rx_packets - tx_packets

    Change-Id: I510a351e899cdf9a1f366d632b9f0528b1d9dcce
    Signed-off-by: Abhijit Sinha <abhijit.sinha@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index faee281..2ed8cb5 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit faee281ab73e49629265fe66dcfdd456d79be2bc
+Subproject commit 2ed8cb5009d69f8aa12853137c04544fa3956fbe