In a callout's classifyFn, one can use the following code to get the remote IP address:
inFixedValues->
incomingValue[FWPS_FIELD_ALE_AUTH_CONNECT_V4_IP_REMOTE_ADDRESS].value.uint32;
// IPv4
or
inFixedValues->
incomingValue[FWPS_FIELD_ALE_AUTH_CONNECT_V6_IP_REMOTE_ADDRESS].value.byteArray16;
// IPv6
However, I can't find any documentation to specify the "byte order" of the IP address from MSDN, OSR, etc.
The following link is the same question as mine, but there was no answers.