Update git submodules

* Update docs/submodules/apex from branch 'stable/danube'
  - Updates vpp and honeycomb version

    The patches in vpp address acl configuration
    issues. A matching honeycomb is needed for
    opendaylight scenarios.

    Change-Id: Ib32dd976170d22fc4dcf4f651433b646461000b6
    Signed-off-by: juraj.linkes <jlinkes@cisco.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 8d69ed9..c454fca 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 8d69ed9b013375ecdab2fb6ddaba3ee0c71079af
+Subproject commit c454fcae3b18b4a31b57cd4d843844241a9c6cdf