socket: Ignore collection errors for now

We can do it since we may not want to dump the missed sockets.
But later, when we will start dumping containers, we'll better
fail here, rather than in the dump stage.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>