When we restore ipv6 addresses, they go through a “tentative” phase
and sockets could not be bound to them in this moment.

v2: add more comments in code
Reported-by: Ross Boucher <boucher@gmail.com>
Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>