package/bind: security bump to version 9.11.6-P1

package/bind: security bump to version 9.11.6-P1

Fixes the following security issues:

 - CVE-2018-5743: Limiting simultaneous TCP clients is ineffective
   https://kb.isc.org/docs/cve-2018-5743

 - CVE-2019-6467: An error in the nxdomain redirect feature can cause
   BIND to exit with an INSIST assertion failure in query.c
   https://kb.isc.org/docs/cve-2019-6467

 - CVE-2019-6468: BIND Supported Preview Edition can exit with an
   assertion failure if nxdomain-redirect is used
   https://kb.isc.org/docs/cve-2019-6468

Add an upstream patch to fix building on architectures where bind does not
implement isc_atomic_*.

Upstream moved to a 2019 signing key, so update comment in .hash file.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>