Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Fix duration value for IXIA traffic item

    Removed code that overrides duration value in the update_frame
    function

    JIRA: YARDSTICK-1369

    Change-Id: Ice06e4fbba4ec93ae086671a2530d521510f89da
    Signed-off-by: Myron Sosyak <myronx.sosyak@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index c4e5cb9..f0bf7df 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit c4e5cb946f068c59ebf29274cdf4c9f860a0b07a
+Subproject commit f0bf7dfe6c6eac91da27c72e2dc31166269f533b