Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "pktgen: speedup unittest, mock time.sleep"
  - pktgen: speedup unittest, mock time.sleep

    Change-Id: I0c6f6b68b30ae72887666a3b9e994dabf7c6a71d
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 2945003..48c0cb1 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 2945003ca74fd3d73621c9e1745dd1662b88c2df
+Subproject commit 48c0cb1b5f3ccd023df1c4ae708236d2f459bfa8