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.
git-svn-id: svn://svn.freebsd.org/base/stable/10@288048
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