Option type.
'ascii' means using the ascii string that is defined
by hpnicfDhcpServer2PoolOptAscii to fill in the option.
'hex' means using the hex string that is defined by
hpnicfDhcpServer2PoolOptHexStr to fill in the option.
'ip' means using the IP string that is defined by
hpnicfDhcpServer2PoolOptIPStr to fill in the option.