Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Merge "delete old ipv6 files"
  - delete old ipv6 files

    JIRA: DOVETAIL-452

    since https://gerrit.opnfv.org/gerrit/#/c/34577/ merged
    new ipv6 C&C documents are there, delete the old ones.

    Change-Id: Ic16cf03b3febd7cca158555e11ecd817ffc61139
    Signed-off-by: MatthewLi <matthew.lijun@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index cbf8b9e..fc706f5 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit cbf8b9e32d57f30fed5a6b1bba971fd530e65520
+Subproject commit fc706f5c364f9ad2f9199cdce1fb85cd3c2bfc1f