Callout Function
A callout function is a function that is implemented by a callout driver that is one of the functions that defines a callout. A callout consists of the following list of callout functions:
A notifyFn function to process notifications.
A classifyFn function to process classifications.
A flowDeleteFn function to process flow deletions (optional).
The filter engine calls a callout's callout functions so that the callout can process the network data.