Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Adding multi-port support for ixia taffic generator"
  - Adding multi-port support for ixia taffic generator

    Change-Id: Ic8aa130f3cdc7bd8dec39d06a6b824340bf658b2
    Signed-off-by: Deepak S <deepak.s@linux.intel.com>
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 624e4d4..c56ca9c 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 624e4d44b60b08deece8ed957829734698250368
+Subproject commit c56ca9c1dccaa11a2ff3af588b45d85207fb1e40