ch4

1. use getaddrinfo() to get all the struct sockaddr info

2. Change AF_INET to AF_INET6. Change PF_INET to PF_INET6.

3. Change INADDR_ANY assignments to in6addr_any assignments

4. Instead of inet_aton() or inet_addr(),use inet_pton()

5. inet_ntoa(),use inet_ntop()

6. etc...