Update git submodules

* Update docs/submodules/apex from branch 'stable/danube'
  - Remove workaround for vhost-user binding

    A fix (https://review.openstack.org/#/c/476947/) for
    bug https://bugs.launchpad.net/networking-odl/+bug/1696968
    has already been merged, no need for this workaround anymore.

    Change-Id: I8e0657e8cf8dcd2045015e086fe591ec50da62d3
    Signed-off-by: juraj.linkes <jlinkes@cisco.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 59450b3..30fbb00 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 59450b35d3fddded17b125da4c82f8153585f16d
+Subproject commit 30fbb001c3efd19781403a15176f240f0c027036