Option type.
'ascii' means using the ascii string that is defined by
hpnicfDhcpServer2OptionAscii to fill in the option.
'hex' means using the hex string that is defined by
hpnicfDhcpServer2OptionHexStr to fill in the option.
'ip' means using the IP string that is defined by
hpnicfDhcpServer2OptionIPStr to fill in the option.