unix_process_name() are called when sockets are being collected,
but at this moment we don't have socket descriptors.

A socket descriptor is reuired to get mnt_id, what will allow to resolve
a socket path in its mount namespace.
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>