Update git submodules

* Update docs/submodules/sfc from branch 'stable/euphrates'
  - Move to sfc_nsh_euphrates image

    To create the four SFs we will use the sfc_nsh_euphrates image. This image is
    like the sfc_nsh_danube but modifying the vxlan_tool which now has the
    important fix:

    https://git.opendaylight.org/gerrit/#/c/64116/

    Change-Id: I396b5523b7243472b6d05b62d831837938067422
    Signed-off-by: Manuel Buil <mbuil@suse.com>

diff --git a/docs/submodules/sfc b/docs/submodules/sfc
index 062e144..b4d2cde 160000 (submodule)
--- a/docs/submodules/sfc
+++ b/docs/submodules/sfc
@@ -1 +1 @@
-Subproject commit 062e1449d1dca89a1771dabc42d7fff44232a657
+Subproject commit b4d2cde30b7854ed239ac9836748781ce5f3e552