Three parts.

Proc: open of map_files' link doesn't work on sockets. We fstatat
it and check that it's a socket (it will be packet), then save
the socket inode on vma_area.

Dump: we resolve socket inode to socket id and save it on vma.
We use id, not inode, since on restore we'll have to mmap some
opened file, not just abstract socket with inode.

Restore: when reading vma-s we just need to find out on what fd
the respective packet socket is opened (i.e. -- no map-and-close
sockets supported by now) and dup() it to let restorer mmap it
back.

All this make it possible to c/r the tcpdump tool!
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>