Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Add IxNextgen API for creating Vlans configurations

    New IxNextgen API allows to configure Vlans(vlan id, priority, tp id)
    to Ethernet layer of device group.

    JIRA: YARDSTICK-1420

    Change-Id: I1c5fe37b5beb11daf1c539933fcad60832553bb9
    Signed-off-by: Serhiy Pshyk <serhiyx.pshyk@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index e625e16..7ab7287 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit e625e162c2e4f817f1bc6a440d85b3cc59272ac4
+Subproject commit 7ab7287fc0332b9a592d2bbf86c646e3b1b3058b