Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Replace assert statements in PipelineRules"
  - Replace assert statements in PipelineRules

    The class PipelineRules uses assert statements to check the correctness
    of an input parameter IP address. This commit will modify these lines
    to use a dedicated function "common.utils.make_ipv4_address".

    JIRA: YARDSTICK-966

    Change-Id: I1c4cc439a7716d36548125c87dfb0bc200714a56
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 0b7647a..af0a6a7 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 0b7647a5a6c85a8a1762ec4482004107989c8550
+Subproject commit af0a6a7593534849626000632b2262cf5fe76db7