nextAsync
Asynchronously retrieves the next #GSocketAddress from @enumerator and then calls @callback, which must call g_socket_address_enumerator_next_finish() to get the result.
It is an error to call this multiple times before the previous callback has finished.
Parameters
cancellable
optional #GCancellable object, null to ignore.
callback
a #GAsyncReadyCallback to call when the request is satisfied