bind: security bump to version 9.9.7-P2

Fixes CVE-2015-5477 - An error in handling TKEY queries can cause named
to exit with a REQUIRE assertion failure.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>