Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Terminate the ixia traffic generator at the end of the test run

    Change-Id: I80501ab3662a58930939d849f0bde0e810154a39
    Signed-off-by: Deepak S <deepak.s@linux.intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 7e2cf50..8b12695 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 7e2cf50af684b10779430f52c01b378f7c796012
+Subproject commit 8b12695ca8a529484409556d244cbf5f015eca8f