kea: upgrade 2.6.1 -> 2.6.3

kea: upgrade 2.6.1 -> 2.6.3

ReleaseNotes:
https://downloads.isc.org/isc/kea/2.6.2/Kea-2.6.2-ReleaseNotes.txt
https://downloads.isc.org/isc/kea/2.6.3/Kea-2.6.3-ReleaseNotes.txt

Security fixes:
CVE-2025-32801
CVE-2025-32802
CVE-2025-32803

License-Update: Update copyright years

* Drop backport patches.

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>