Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r235317:

General mdoc(7) and typo fixes.

PR: 167776

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

If none of the watchdogs supports the requested timeout value, the
code returns EOPNOTSUPP, not EINVAL.

- Eliminated hard sentence breaks.
- Fixed spelling of EINVAL.
- Sorted sections.

Add missing El.

MFC after: 1 week

Align the interfaces for the various watchdogs and make the interface
behave as expected.

Also:
- Return an error if WD_PASSIVE is passed in to the ioctl as only
WD_ACTIVE is implemented at the moment. See sys/watchdog.h for an
explanation of the difference between WD_ACTIVE and WD_PASSIVE.
- Remove the I_HAVE_TOTALLY_LOST_MY_SENSE_OF_HUMOR define. If you've
lost your sense of humor, than don't add a define.

Specific changes:

i80321_wdog.c
Don't roll your own passive watchdog tickle as this would defeat the
purpose of an active (userland) watchdog tickle.

ichwd.c / ipmi.c:
WD_ACTIVE means active patting of the watchdog by a userland process,
not whether the watchdog is active. See sys/watchdog.h.

kern_clock.c:
(software watchdog) Remove a check for WD_ACTIVE as this does not make
sense here. This reverts r1.181.

o Document /dev/fido.

PR: docs/85425
Approved by: phk
MFC after: 2 weeks

Yield to ru's ninja-like manpage skills and update watchdog(4) to
look more like other manpages. Move some content around, use an EXAMPLES
section, etc.

Submitted by: ru

Add more .Dv markup.

Add missing .Dv markup and a comma.

Fix up a little language. Remove reference to sysctl(9). Fix reference to
watchdog(9) (was watchdogd(9)).

Rename the WATCHDOG option to SW_WATCHDOG and make it use the
generic watchdoc(9) interface.

Make watchdogd(8) perform as watchdog(8) as well, and make it
possible to specify a check command to run, timeout and sleep
periods.

Update watchdog(4) to talk about the generic interface and add
new watchdog(8) page.

- Add a software watchdog facility.

This commit has two pieces. One half is the watchdog kernel code which lives
primarily in hardclock() in sys/kern/kern_clock.c. The other half is a userland
daemon which, when run, will keep the watchdog from firing while the userland
is intact and functioning.

Approved by: jeff (mentor)