fix: populate ldns submodule and add autotools to LDNS build stage

- Re-cloned zonemaster-ldns with --recurse-submodules so the bundled
  ldns C library source (including Changelog and configure.ac) is present
- Added autoconf, automake, libtool to Dockerfile.backend ldns-build stage
  so libtoolize + autoreconf can generate ldns/configure during make

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

zonemaster-ldns/ldns/contrib/DNS-LDNS/lib/DNS/LDNS/RData.pm

@@ -0,0 +1,91 @@
+package DNS::LDNS::RData;
+
+use 5.008008;
+use strict;
+use warnings;
+
+use DNS::LDNS;
+
+our $VERSION = '0.61';
+
+sub new {
+    my ($class, $type, $str) = @_;
+    return _new($type, $str);
+}
+
+sub cat {
+    my ($self, $other) = @_;
+
+    my $s = _cat($self, $other);
+    $DNS::LDNS::last_status = $s;
+    return $s;
+}
+
+sub nsec3_hash_name {
+    my ($self, $algorithm, $iterations, $salt) = @_;
+    return DNS::LDNS::GC::own(
+	$self->_nsec3_hash_name($algorithm, $iterations, $salt), $self);
+}
+
+sub DESTROY {
+    DNS::LDNS::GC::free($_[0]);
+}
+
+1;
+__END__
+
+=head1 NAME
+
+DNS::LDNS::RData - Rdata field or a dname in an rr
+
+=head1 SYNOPSIS
+
+  use DNS::LDNS ':all'
+
+  my rd = new DNS::LDNS::RData(rdf_type, str)
+  rd2 = rd->clone
+
+  rdf_type = rd->type
+  rd->set_type(rdf_type)
+
+  rd->print(\*FILE)
+  str = rd->to_string
+
+  count = rd->label_count
+  rd2 = rd->label(pos)
+
+  bool = rd->is_wildcard
+  bool = rd->matches_wildcard(wildcard)
+  bool = rd->is_subdomain(parent)
+
+  rd2 = rd->left_chop
+
+  status = rd->cat(rd2)
+  rd->compare(rd2)
+  rd2 = rd->address_reverse
+  rd2 = rd->dname_reverse
+
+  rd2 = rd->nsec3_hash_name(name, algorithm, iterations, salt)
+
+  epoch = rd->to_unix_time
+( epoch = rd->2native_time_t )
+
+  rr_type = rd->to_rr_type
+
+=head1 SEE ALSO
+
+http://www.nlnetlabs.nl/projects/ldns
+
+=head1 AUTHOR
+
+Erik Pihl Ostlyngen, E<lt>erik.ostlyngen@uninett.noE<gt>
+
+=head1 COPYRIGHT AND LICENSE
+
+Copyright (C) 2013 by UNINETT Norid AS
+
+This library is free software; you can redistribute it and/or modify
+it under the same terms as Perl itself, either Perl version 5.14.2 or,
+at your option, any later version of Perl 5 you may have available.
+
+=cut