Allow the user to configure one host/mac addr for the whole box (default)
where, if configured, the CfgHostAddress is used (becomes HostAddress)
otherwise if left unconfigured the Host address is discerned from the
backplane serial number. If Multiple host is Enabled and the host number is
configured in the interface record the configured value is used as the
hostid/mac addr of the interface (except Token Ring which can't go into
promiscous mode, uses Token Ring Mac as hostid/mac of interface). If the
host number in left unconfigured then the hostid/mac is gotten from the
mac of the circuit.