bind: Update to 9.11.21

bind: Update to 9.11.21

For details see:
https://downloads.isc.org/isc/bind9/9.11.21/RELEASE-NOTES-bind-9.11.21.html

"Bug Fixes

    named could crash when cleaning dead nodes in lib/dns/rbtdb.c that
    were being reused. [GL #1968]

    Properly handle missing kyua command so that make check does not
    fail unexpectedly when CMocka is installed, but Kyua is not. [GL
    #1950]

    The validator could fail to accept a properly signed RRset if an
    unsupported algorithm appeared earlier in the DNSKEY RRset than
    a supported algorithm. It could also stop if it detected a malformed
    public key. [GL #1689]"

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>