USBNSH is not working on STM32F4Discovery

I decided to help Ed to fix to USB issue #6531 and decided to test the USB on STM32F4Discovery board.

Unfortunately version 10.3.0, didn't work, then I decided to test 10.2.0, also didn't work, version 10.0.0 shows the "nsh>" but doesn't work and display the message: "nsh: nsh_session: readline failed: 9"

The only working version was 9.1.1! It means it was working around Dec 2020, but stopped to work some time later.

Once again we need to find a way to automatically test these boards, unfortunately only getting a board passing on CI test is not enough.

These are the step to duplicate the issue
```
$ ./tools/configure.sh stm32f4discovery:usbnsh
$ make
1) Flash the firmware in the board
2) Connect a Micro USB cable to CN5 connector
3) It will create a /dev/ttyACM0 on your computer, then configure minicom to use this /dev/ttyACM0 port
4) On minicom press ENTER 3 times, the "nsh>" will not show up
```