Default to use 10 seconds as nap interval instead of 1.

Previously, we have a nap interval of 1 second while we have a timeout of
128 seconds by default, which could be an overkill, and for some hardware
the patting action may be expensive.

Note that the choice of nap interval is still arbitrary.  We preferred
a safe value where even when the system is very heavily loaded, the
watchdog should not shoot the system down if it's not really hung.
According to the manual page of Linux's watchdog daemon, the nap interval
time of theirs is 10 seconds, which seems to be a reasonable value --
according to Intel documentation AP-725 (Document Number: 292273-001),
ICH5's maximum timeout is about 37.5 seconds, which the ichwd(4) driver
would set when we requested 128 seconds (although it should probably
feed back this as an error and do not set the timeout).  Since that's
the shortest maximum value, 10 seconds seems to be a right choice for
us too.

Discussed with:	alfred
MFC after:	1 month


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274583 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f