Update git submodules

* Update docs/submodules/ipv6 from branch 'master'
  - Update the index file of user guide

    Change-Id: If0f29f9385ecc3feb8a505284af4780c6757f280
    Signed-off-by: BIN HU <bin.hu@att.com>

diff --git a/docs/submodules/ipv6 b/docs/submodules/ipv6
index 4320184..2ee0750 160000 (submodule)
--- a/docs/submodules/ipv6
+++ b/docs/submodules/ipv6
@@ -1 +1 @@
-Subproject commit 43201848abcec2c591e275f4adef073e1d015d07
+Subproject commit 2ee07505b65b7dcb97c21fba56e59c70b6b34979