Function openthread_sys::otPlatDebugUart_kbhit

pub unsafe extern "C" fn otPlatDebugUart_kbhit() -> c_int

Poll/test debug uart if a key has been pressed. It would be common to a stub function that returns 0.

MUST be implemented by the platform

@retval zero - nothing ready @retval nonzero - otPlatDebugUart_getc() will succeed.