Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Update tempest bgpvpn test case

    For functest.tempest.bgpvpn, it has been run by Functest networking-bgpvpn since
    Functest Gambia. Also the test list has been updated.

    Using Functest smoke image to run networking-bgpvpn test case.
    The test case list can be found here:
    http://testresults.opnfv.org/test/api/v1/results?case_name=networking-bgpvpn&version=gambia

    Change-Id: I18dd0fa24011c8805c2138d0efcb74474051c6c8
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index b4e6a75..1540d41 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit b4e6a756ebeb019048cb03a0562534870b772cae
+Subproject commit 1540d41ec9291d61c1cd5b5d2f347d1d8f9c3dbe