Hardware address for a rule.
The structure of the OCTET STRING is H-H-H... while H indicates 4
hexadecimal characters except that the last H indicates 2 or 4
hexadecimal characters.
The SET operation to this object ought to be with the SET operation
of hpnicfDhcpServer2RuleHwAddrMask together, and any SET operation
alone to this object will be regarded as an invalid operation.