Yu Watanabe

Please also rebase.

Force-pushed: - fixed genl family name, - sort genl attributes, - dropped netlabelctl from mkosi again, as it is for networkd-test.py, not systemd-networkd-tests.py, - many fixes and cleanups for systemd-networkd-tests.py,...

@mrc0mmand Could you install netlabel_tools in CentOS CI environments, and restart CentOS CIs?

LGTM. But still CentOS CI is in red.

> there are seccomp issues on Jammy that need to be investigated. Is it filed somewhere? > Also Bullseye has 0.56.2, I am not familiar, but bullseye-backports cannot be used??

@medhefgo > Might as well deal with `FIXME: Use fs.stem() with meson >= 0.54.0` in the main meson file too. :P Thanks. Addressed.

@bluca > > > Also Bullseye has 0.56.2, > > > > I am not familiar, but bullseye-backports cannot be used?? > > That's not enabled by default, we should...

According to the suggested policy in #23403, we can cut off Ubuntu focal (after #23213), but Ubuntu impish (21.10) needs to be supported... BTW, what the meaning of the version...

> > @bluca > > > > > Also Bullseye has 0.56.2, > > > > > > > > > > > > I am not familiar, but bullseye-backports...

(BTW, I neither request this to be merged within few days nor soon after v251 is released. This is just a proposal and WIP PR.)