man: fix incorrect volume numbers in internal man page references

man: fix incorrect volume numbers in internal man page references

Some ambiguity (e.g., same-named man pages in multiple volumes)
makes it impossible to fully automate this, but the following
Python snippet (run inside the man/ directory of the systemd repo)
helped to generate the sed command lines (which were subsequently
manually reviewed, run and the false positives reverted):

from pathlib import Path

import lxml
from lxml import etree as ET

man2vol: dict[str, str] = {}
man2citerefs: dict[str, list] = {}

for file in Path(".").glob("*.xml"):
    tree = ET.parse(file, lxml.etree.XMLParser(recover=True))
    meta = tree.find("refmeta")
    if meta is not None:
        title = meta.findtext("refentrytitle")
        if title is not None:
            vol = meta.findtext("manvolnum")
            if vol is not None:
                man2vol[title] = vol
            citerefs = list(tree.iter("citerefentry"))
            if citerefs:
                man2citerefs[title] = citerefs

for man, refs in man2citerefs.items():
    for ref in refs:
        title = ref.findtext("refentrytitle")
        if title is not None:
            has = ref.findtext("manvolnum")
            try:
                should_have = man2vol[title]
            except KeyError:  # Non-systemd man page reference?  Ignore.
                continue
            if has != should_have:
                print(
                    f"sed -i '\\|<citerefentry><refentrytitle>{title}"
                    f"</refentrytitle><manvolnum>{has}</manvolnum>"
                    f"</citerefentry>|s|<manvolnum>{has}</manvolnum>|"
                    f"<manvolnum>{should_have}</manvolnum>|' {man}.xml"
                )