Add support for logging security related events

This patch introduces the LOG_CONSOLE syslog facility for logging common
events.  In industrial applications aiming for IEC 62443 compliance the
following events are central for system observability:

- Change of runlevel - i.e., starting up, shutting down, upgrade, etc.
  Facility: console, severity: notice
- Service starting
  Facility: console, severity: notice
- Service restarting
  Facility: console, severity: notice
- Service stopping
  Facility: console, severity: notice
- Service failed to start
  Facility: console, severity: warning

The use of facility console for this makes it easier to filter out when
forwarding syslog messages from an embedded system to a remote log sink.
Otherwise messages of facility daemon would be used, which include a lot
more, and mostly irrelevant, information.

Signed-off-by: Jonas Holmberg <jonas.holmberg@westermo.se>
Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/log.h

@@ -26,6 +26,11 @@
 
 #include <syslog.h>
 
+/* Local facility, unused in GNU but available in FreeBSD or sysklogd >= 2.0 */
+#ifndef LOG_CONSOLE
+#define LOG_CONSOLE  (14<<3)
+#endif
+
 /*
  * Developer error and debug messages, otherwise --> use logit() <--
  *                                                   ~~~~~~~~~~~