Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Clean up noifupdown support patch

    The patch has been merged to upstream linux formula.

    Change-Id: I09f96be920c5c3ecd09fd2ab132e25519902239b
    Signed-off-by: Michael Polenchuk <mpolenchuk@mirantis.com>

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 52e37b7..a6bc08b 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 52e37b795bb975b1cb3bf1f684b009848c50a2d6
+Subproject commit a6bc08b2be51b069b629d357a44cfa5979f09c2a