Enable or Disable the Serial Port

When enabling or disabling the serial port, make sure you have followed the rules below:

Include all the following header files:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

Make sure you use standard functions to open and close the files you need.
```
int open(const char *pathname, int flags);
int close (int fd)
```