Add the official UDP_echo sample function based on the code generated last time with STM32CubeIDE, and send one more after each receipt.

Current problems

• It was so unstable that after a while it would not be connected or pinged; (2020/4/7: The current test is a problem with the network debugging assistant. Today, a new assistant has been tested for 3 hours without interruption.)
• Need to add debugging output, easy to debug, and add an indicator light; (2020/4/7: Use ITM directly to implement printf to print information, add a task using blink.)
• Network debugging assistant in UDP, after the listener is turned off, it cannot be enabled again. You need to turn off the software and then enable it.
• Network debugging Assistant does not support Sending Chinese;