binfmt: add logging information

binfmt: add logging information

In delete_rule(), we already checked that the rule name is a valid file name
(i.e. no slashes), so we can just trivially append.

Also, let's always reject rules that we would later fail to delete. It's
probably better to avoid such confusion.

And print the operations we do with file name and line number. I hope this
helps with cases like https://github.com/systemd/systemd/pull/21178. At least
we'll know what rule failed.

$ sudo SYSTEMD_LOG_LEVEL=debug build/systemd-binfmt
Flushed all binfmt_misc rules.
Applying /etc/binfmt.d/kshcomp.conf…
/etc/binfmt.d/kshcomp.conf:1: binary format 'kshcomp' registered.