private synchronized void portScanned(int port, boolean open) {
        if (open) {
            openPortsFound.add(port);
        }
        if (portListener != null) {
            portListener.onResult(port, open);
        }
    }
Perform an asynchronous (non-blocking) port scan

@param portListener - the listener to fire portscan results to.
@return - this object so we can cancel the scan if needed
library/src/main/java/com/stealthcopter/networktools/PortScan.java