unix: Do not autobind unnamed unix sockets

addlen equal to sizeof(addr.sun_family) leads
to autobinding of socket.

If it had been autobinded when we dumped it,
name.len wouldn't have been zero. So, this
binding is wrong. Fix that.

v2: Merge two conditional branches together
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>