MFC 281734-281736,287997-287998:

• Fix a crash on a rpc entry when an IPv6 address is explicitly specified in -a flag.

• Fix a bug that sockaddr_in was used where sockaddr_in6 should have been used. This was not actually harmful because offsetof(struct sockaddr_in, sin_port) is equal to offsetof(struct sockaddr_in6, sin6_port).

• Remove unused union p_un.

• Use NI_MAXHOST-long buffer for getnameinfo(). Although INET6_ADDRSTRLEN was designed to hold the longest IPv6 address in IPv4-mapped address format a long time ago, getnameinfo() can return scope identifier in addition to it.