Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Splitting IPv6 tests in API and scenario tests

    Spliting the IPv6 test case in Tempest API tests and scenario tests. The
    API tests will be promoted to mandatory while the scenario tests will
    remain optional.

    JIRA: DOVETAIL-677

    Change-Id: If3dca5ecf2ce5c9e02de5c6d45e674da029b609f
    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 60e4604..964b0aa 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 60e46040086cc8d866bfea565ae3d0b5a52db265
+Subproject commit 964b0aaceaff268d6e12d50d92ed766b8e6cd2d4