The nng_aio_stop() function stops the asynchronous I/O operation associated with aio by aborting with
NNG_ECANCELED, and then waits for it to complete or to be completely aborted, and for the callback
associated with the aio to have completed executing.
Further calls to nng_aio_begin() using this aio will return false.
It is safe to call this for an aio, even when no operation is currently pending for it.
Tip
When multiple asynchronous I/O handles are in use and need to be shut down, it is safest to stop all
of them, before deallocating any of them with nng_aio_free(), particularly if the callbacks might
attempt to reschedule additional operations.