Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - Use "protocol" parameters in iperf3 yaml and task file

    JIRA: YARDSTICK-755

    There is a history problem that iperf use udp to set a net protocol.
    This code will change it to protocol.
    so you could use 'tcp','udp' and other protocol.

    Change-Id: I1a101013dfe58165a3ed08aa77f0aa2f73d57a12
    Signed-off-by: Ace Lee <liyin11@huawei.com>
    (cherry picked from commit 10f85b332c4b1f55e651aeb9c45b328e1ebdc2af)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index d6b1489..4608b2d 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit d6b148980fb78d99ed99985bf578ce285ead51d6
+Subproject commit 4608b2d7a467344cde6208eaa5d0db58d7d7d42f