The value of the object tmnxDhcpSvrSubnetOptionType specifies how
the value of this option in stored in tmnxDhcpSvrSubnetOptionValue.
The value of this object cannot be set to 'domain (5)' when the value
of tmnxDhcpServerCfgAddrType is set to 'ipv4(1)'.
This object is mandatory at creation time.