Frr logs to /var/log/frr without rotation

[troglobit]

Set up Frr with syslog, format rfc5424:

• https://docs.frrouting.org/en/latest/basic.html#clicmd-log-syslog-LEVEL
• https://docs.frrouting.org/en/latest/extlog.html#clicmd-destination-syslog-supports-rfc5424

This will let it log structured logs directly to /dev/log, without passing the non-functional GLIBC syslog() API. Allowing syslogd to both filter, forward, and handle log rotation.