tcp: allow to enable the repair mode for non-listening sockets

The repair mode is used to get and restore sequence numbers and
data from queues. It used to checkpoint/restore connections.

Currently the repair mode can be enabled for sockets in the established
and closed states, but for other states we have to dump the same socket
properties, so lets allow to enable repair mode for these sockets.

The repair mode reveals nothing more for sockets in other states.

Signed-off-by: Andrei Vagin <avagin@openvz.org>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>