Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  to 2bb4fd12a195f32357fafd8b11374118fc336d3c
  - Remove sdnvpn test cases

    Functest removed test case 'bgpvpn' from scope of Hunter release.
    Also remove them from Dovetail for next release.

    The original link of refstack is invalid now. Changing it to interop link.

    Change-Id: I5b686496e106d688b8b3768401be95ac58fa2122
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 47559a6..2bb4fd1 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 47559a6afe2c66ff536c45f61be730991042b68d
+Subproject commit 2bb4fd12a195f32357fafd8b11374118fc336d3c