Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Store packetsize in influxdb

    This allows calculating throughput in Gbps.

    Add: test_pktgen.py

    Change-Id: I7e2132ec71985c14570ef18b952b2264ebf7abbc
    JIRA: YARKSTICK-611
    Signed-off-by: Jing Zhang <jing.c.zhang@nokia.com>
    (cherry picked from commit 639450d91ab409f70b6f119291197da40b1d5f0b)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index f4f7104..478a499 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit f4f7104e942988e6cf294c3ad80d1a96dc051aaa
+Subproject commit 478a499e8cb048abf434559c8d47259ec238ed24