* ArduinoOTA would stop receiving any packets if the port received a zero-length UDP packet, commonly sent by network scanners like nmap. Fixed to flush() after every call to parsePacket(), even if read length is 0.
Additionally, added length checking to fix a potential buffer overflow in parseInt().
Finally, added an end() method that stops the OTA listener and releases resources.
* Only end MDNS in end() if mdns mode is enabled.
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