libxml2: Ignore CVE-2016-3709

This is fixed via a revert in 2.9.11 [1]

[1] https://gitlab.gnome.org/GNOME/libxml2/-/commit/c1ba6f54d32b707ca6d91cb3257ce9de82876b6f



Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 131b7010)
Signed-off-by: Steve Sakoman <steve@sakoman.com>