Basic Socket API

We introcuded sin6_scope_id support
linux-2.4.x and glibc-2.2.x
We cleaned up bind(2) to let it behave as we expected.
IPv6 and IPv4 co-exist on the same port.
IPV6_V6ONLY socket option introduced in RFC2553bis
SO_REUSEPORT-like behaviour of SO_REUSEADDR should be restricted only for multicasts.