watchdog: stop watchdog first on startup

watchdog: stop watchdog first on startup

Some watchdog implementations may do things other than issue
a reboot on a watchdog timeout.  In this case, there's the
possibility of restarting this program from the state of
the watchdog device not being properly stopped (done by writing
a 'V' and closing the device).  Since it wasn't stopped, the
driver may not be able to restart the watchdog when this program
reopens it and starts pinging it.

To fix this, the code will always first issue the stop when it
starts up.

function                                             old     new   delta
shutdown_on_signal                                     -      32     +32
watchdog_main                                        268     298     +30
shutdown_watchdog                                      -      25     +25
watchdog_shutdown                                     41       -     -41
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 1/0 up/down: 87/-41)             Total: 46 bytes

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>