Don't call callback or submit new transfers once streaming stops.

This stops the RX callback from being called again with further data
once it has returned nonzero, or after a transfer had an error status.

host/libhackrf/src/hackrf.c

@@ -1737,7 +1737,7 @@ static void LIBUSB_CALL hackrf_libusb_transfer_callback(struct libusb_transfer*
 			.tx_ctx = device->tx_ctx
 		};
 
-		if( device->callback(&transfer) == 0 )
+		if (device->streaming && device->callback(&transfer) == 0)
 		{
 			// Take lock to make sure that we don't restart a
 			// transfer whilst cancel_transfers() is in the middle