Update git submodules

* Update docs/submodules/apex from branch 'master'
  - Physical interface type note

    add ovs_bridge as needed compared to earlier version

    Change-Id: I1d0c6df9d1f47b0c98a3c1a8bf3a04eb5f53aff2
    Signed-off-by: Tomi Juvonen <tomi.juvonen@nokia.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index ae22c33..d6af6ae 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit ae22c3358b53a68b68de7d3ac5d6f56a1c384b61
+Subproject commit d6af6ae3c5a38e752a8df664b1d5aa3d49d1fa57