Update git submodules

* Update docs/submodules/apex from branch 'stable/danube'
  - Migrates quagga install to build time

    It is OK to have quagga installed at build time, we just want to avoid
    enabling it unless quagga is deployed.

    Change-Id: I41899d697a24976c3b169b3b8f5eef5c0df6bed4
    Signed-off-by: Tim Rozet <trozet@redhat.com>
    (cherry picked from commit f50f469ff5db3fd54c49cc932ff7791c406891cf)

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 6557a83..c6b4b82 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 6557a832f652ac8a57ef9ad4c7b5cded3f9a7db2
+Subproject commit c6b4b82f7f9d13721ae141b570221a20b53117ce