Update git submodules

* Update docs/submodules/apex from branch 'master'
  - Merge "nosdn-fdio scenarios fixes"
  - nosdn-fdio scenarios fixes

    - pin vpp/networking-vpp versions
    - Add external_network_bridge config back to puppet-neutron

    Change-Id: Ia58fb55638390757ea3350b2921897c4d315f9b5
    Signed-off-by: Feng Pan <fpan@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index e6a9d7c..7d77be7 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit e6a9d7cebc9f6083a72863102138ab76a75ae3c9
+Subproject commit 7d77be7913b633291e6d864b0a3a2db7e9c18a0b