Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Addition of NSB Prox test documentation of vPE and LW-AFTR test cases"
  - Addition of NSB Prox test documentation of vPE and LW-AFTR test cases

    YARDSTICK-840

    NSB Prox test documentation of vPE and LW-AFTR test cases documenation.

    Change-Id: Ic6da6546faf0494fdee71962a515083e6e10a410
    Signed-off-by: Daniel Martin Buckley <daniel.m.buckley@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 36c24ec..23de47c 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 36c24ec9fc68c081d0bca507cff3ec81f8a001dc
+Subproject commit 23de47c859f84b7616d8345e96852bde83cd5ab5