Improvements of bind(2)

Reworked
Restrictions of SO_REUSEADDR
SO_REUSEPORT-like behavior are only for multicasts
Both should be made by same uid
against binding-closer type DoS
conflicts with device-specific bind(2)
use SO_REUSEADDR
Introduction of IPV6_V6ONLY
set IPV6_V6ONLY to the IPv6 socket
Both should be made by same uid