kea: fix CVE-2025-11232

kea: fix CVE-2025-11232

Backport a patch from upstream to resolve CVE-2025-11232:

  Invalid characters cause assert

  To trigger the issue, three configuration parameters must have
  specific settings: "hostname-char-set" must be left at the default
  setting, which is "[^A-Za-z0-9.-]"; "hostname-char-replacement" must
  be empty (the default); and "ddns-qualifying-suffix" must NOT be empty
  (the default is empty). DDNS updates do not need to be enabled for
  this issue to manifest. A client that sends certain option content
  would then cause kea-dhcp4 to exit unexpectedly.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>