kea: bump to 3.0.3

kea: bump to 3.0.3

3.0.3 is a security/vulnerability release on the stable 3.0 series.

Notable fixes since 3.0.2:

* **CVE-2026-3608** — A large number of bracket pairs in a JSON payload
  sent to any endpoint caused a stack overflow during recursive parsing.
  The exploit does not need a syntactically valid command, so it bypasses
  RBAC and the command filters on the High-Availability endpoints
  (upstream #4275 / #4288 / #4387).

* Null dereference when configuring the Control Agent with a socket
  entry that lacks the mandatory ``socket-name`` is now caught
  (#4388, #4365).

* UNIX command sockets are created group-writable so Stork 2.4.0+ and
  other tooling using the configured group can talk to the daemon
  (#4398, #4260).

Upstream's release notes flag "no incompatible changes" and "no known
issues" for this bump.

All current patches still apply cleanly.

Release notes:
https://ftp.isc.org/isc/kea/3.0.3/Kea-3.0.3-ReleaseNotes.txt

Signed-off-by: Alexandru Ardelean <redacted>