Some hardware watchdogs report a timeout of 0 which causes vyos watchout timeout validation to fail.

Test senario:

# Confirm watchdog is available:
$ wdctl
> Device:        /dev/watchdog0
> Identity:      iTCO_wdt [version 0]
> Timeout:       30 seconds
> Timeleft:       2 seconds

# Check kernel reported timeout
grep '' /sys/class/watchdog/watchdog0/*_timeout
> /sys/class/watchdog/watchdog0/max_timeout:0
> /sys/class/watchdog/watchdog0/min_timeout:0

# Setup watchdog in VyOS:
set system watchdog
confirm
> [ system watchdog ]
> 'timeout' must be <= 0 seconds (driver maximum)

Expectation is the watchdog should be enabled, but currently rejected because default timeout is not accepted. No value of set system watchdog timeout 30 is accepted because VyOS is reading 0 timeout from kernel.

VyOS should ignore 0 values of timeout

/sys/class/watchdog/watchdog0/max_timeout:0
/sys/class/watchdog/watchdog0/min_timeout:0

Link: https://vyos.dev/T7101 (introduction of watchdog feature)