Update git submodules

* Update docs/submodules/nfvbench from branch 'stable/euphrates'
  - Enable referencing for release notes

    Change-Id: I0188c1895d9ad19a0ab862ce7728477c01de6541
    Signed-off-by: Sofia Wallin <sofia.wallin@ericsson.com>

diff --git a/docs/submodules/nfvbench b/docs/submodules/nfvbench
index 124ecd5..c528972 160000 (submodule)
--- a/docs/submodules/nfvbench
+++ b/docs/submodules/nfvbench
@@ -1 +1 @@
-Subproject commit 124ecd5d59869bad3a4f5f53f91f5b9c99051512
+Subproject commit c528972bfe3dbc4100e9b2b486785d2b03599cf8