misc: syslog: Fix calls to openlog() with LOG_KERN facility (BZ #3604)

POSIX states for syslog [1]:

  "Values of the priority argument are formed by OR'ing together a
  severity-level value and an optional facility value. If no
  facility value is specified, the current default facility value is
  used."

So the patch fixes an existing violation of the openlog interface contract
where it is ignoring the facility argument when the value is zero

It allows the use LOG_KERN by calling openlog prior syslog usage.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

[1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html