Assigns a client to the specified target, which receives callbacks when the reachability of the target changes.
- iOS 2.0+
- macOS 10.3+
- tvOS 9.0+
The network reference associated with the address or name to be checked for reachability.
The function to be called when the reachability of the target changes. If
NULL, the current client for the target is removed.
The reachability context associated with the callout. This value may be
TRUE if the notification client was successfully set; otherwise,