All sockets are created with SO_REUSEADDR, it's needed for restoring.
E.g.: A listen socket is created after a connected socket. Both of them
are binded to one port.

So SO_REUSEADDR should be restored, when all sockets on a port were created.

This code creates a structure for each port of one type of sockets
and accounts a number of sockets, which are not restored yet.

Sockets have a hook post_open(), in which it waits when all sockets for
a defined port would be created and then it will restore SO_REUSEADDR.

struct port contains a type (udp, tcp, etc) and a port number.
It doesn't contain family or addr, because it's extra loads of logic,
which doesn't bring a significant profits.

v2: fix according with comments from Pavel
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>