Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Make TRex latency statistics optional"
  - Make TRex latency statistics optional

    Because of performance issues in TRex due to the extra power needed to
    retrieve the latency statistics, this parameter will be optional and disabled
    by default.

    JIRA: YARDSTICK-1388

    Change-Id: I07c0ec7bef86fd438d078cbd6748b98bc8cc0b37
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index aa4e2d2..eea4e0e 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit aa4e2d2645497f04e9e389aacc0381ff776b0125
+Subproject commit eea4e0e9e2261ef27b5884c51d763b71ff324fb9