MFC r221121,221173:

MFC r221121,221173:
- Add the possibility to reuse the already last used timeout when patting
  the watchdog, via the watchdog(9) interface.
- Add the possibility to pat the watchdogs installed via the watchdog(9)
  interface from the kernel.
- Avoid to pass WD_ACTIVE down in the watchdog handlers. All the control
  bit processing should over to the upper layer functions and not passed
  down to the handlers at all.
- Add the watchdogs patting during the (shutdown time) disk syncing and
  disk dumping.

Sponsored by:	Sandvine Incorporated

git-svn-id: svn://svn.freebsd.org/base/stable/8@221939 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f