Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Enable back IPv6 for OVN based scenario

    IPv6 has been disabled recently by default to reduce the attack
    surface of the system, however OVN/Geneve kernel-based tunnels
    require it to function properly.

    [https://www.mail-archive.com/ovs-discuss@openvswitch.org/msg03639.html]

    Change-Id: Ife86dfad77e7899bd28f83a49c361cd8a623597c
    Signed-off-by: Michael Polenchuk <mpolenchuk@mirantis.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 90a4421..2fb56d9 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 90a442136b0aff8380388ac0a94831d0904e3cb8
+Subproject commit 2fb56d96ce6758f73837a67077e50401a09a2b48