Add PacketFlux SiteMonitor Base3 Classic

Requesting support for the Packetflux SiteMonitor Base3 Classic. The OIDs have changed since the SiteMonitor 2.

Vendor documentation/mibs: Documentation for PacketFlux SiteMonitor Base3 Classic
snmpwalk output: SiteMonitor3 snmpwalk - LibreNMS

If you need any further information please let me know.

Thanks.