Fix the watchdog timeout calculation to prevent wrap.  The RPi hardware
can't do a timeout bigger than 15 seconds.  The code wasn't checking for
this and because bitmasking was involved the requested timeout was
basically adjusted modulo-16.  That led to things like a 128 second
timeout actually being a 9 second timeout, which accidentally worked fine
until watchdogd was changed to only pet the dog once every 10 seconds.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275660 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f