Unix sockets may be connected via deleted socket name,
moreover the name may be reused (ie same sun_addr but
different inodes).

To be able to handle them we do a few tricks:

 - when collecting sockets we figure out if "deleted"
   mark is present on the socket and if such we order
   this sockets creation and deletion with mutex, together
   with adding missing directories, and save this descriptors
   in fdstore if there are peers connected to

 - on restore we connect via procfs/fd/X as suggested by
   Andrew Vagin
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>