net/bird2: Update to 2.0.12

Due to some patches accepted in the upstream simplify port.
Make the netlink flavor available for the upcoming 13.2-RELEASE and stable/13.

Changelog: https://bird.network.cz/pipermail/bird-users/2023-January/016560.html

PR: 269553
Reported by: Marek Zarychta <zarychtam@plan-b.pwste.edu.pl>