Update git submodules

* Update docs/submodules/yardstick from branch 'stable/gambia'
  - Merge "Adding Grafana dashboard for visualizing the vEPC default bearer metrics." into stable/gambia
  - Adding Grafana dashboard for visualizing the vEPC default bearer metrics.

    The dashboard will highlight the Network metrics captured from Spirent landslide traffic generator.

    JIRA: YARDSTICK-1350

    Change-Id: I47920446181355a97e875fd82afd633b336c8da6
    Signed-off-by: Carey, Alan <alan.carey@intel.com>
    (cherry picked from commit 5bf76a7a2ead6e8c3a0d8bc05c7ec89d9faaa5a5)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 1d7841d..6227c1a 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 1d7841d21af77492674bebf5675d6f33017baf9f
+Subproject commit 6227c1aadbfd6ad6e5dcbb9c53b2fb1020c94e1f