Add autoconf rules to detect IPv6 availability and some of the neeeded
support functions. Add stubs for getaddrinfo and inet_ntop.
You can disable IPv6 at compile time with
./configure --without-ipv6
Signed-off-by: Karsten Keil <kkeil@suse.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
