Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Update the IPv6 for the remain comments

    JIRA: DOVETAIL-461

    1. Lincoln’s comments about tc018-tc021: change “using DHCPv6” to “using DHCPv6 stateless”
    2. Update tc018-tc025: give more details and modify some misunderstanding about these test cases.
    For more detail, please refer to jira or this patch.

    Change-Id: Ieb7ee9d0b8a31826c7f2f69cb5f209055fd7b928
    Signed-off-by: hongbotian <hongbo.tianhongbo@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index cc034a7..017fb8d 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit cc034a7135cf70f137915f8b55c8ef00ab61e96e
+Subproject commit 017fb8d0d9fc1eed7cbaa7605b3fe8074ef187df