man: fix sd_watchdog_enabled() prototype in man page

https://bugs.freedesktop.org/show_bug.cgi?id=80597
journald: make MaxFileSec really default to 1month

journald.conf(5) states that the default for MaxFileSec is one month,
but the code didn't respect that.
update TODO
libudev: queue - watch entire directory to allow the re-use of the watch descriptor