This will enter or exit listening mode, which opens a Serial connection to get Ethernet credentials over USB, and also listens for credentials over Bluetooth.
// SYNTAX - enter listening mode Ethernet.listen();
Listening mode blocks application code. Advanced cases that use multithreading, interrupts, or system events have the ability to continue to execute application code while in listening mode, and may wish to then exit listening mode, such as after a timeout. Listening mode is stopped using this syntax:
// SYNTAX - exit listening mode Ethernet.listen(false);