Found using linkchecker.
For virtiofsd, the man page is maintained upstream, but doesn't seem to be
available in any of the usual places. So let's link to the Debian version.
systemd.filter I have no idea what it is.
In the troff output, this doesn't seem to make any difference. But in the
html output, the whitespace is sometimes preserved, creating an additional
gap before the following content. Drop it everywhere to avoid this.
Let's systematically make sure that we link up the D-Bus interfaces from
the daemon man pages once in prose and once in short form at the bottom
("See Also"), for all daemons.
Also, add reverse links at the bottom of the D-Bus API docs.
Fixes: #34996
Zbigniew Jędrzejewski-Szmek
Lennart Poettering
Yu Watanabe