tcp: disable repair mode for sockets on rollback (v2)

Currently if a network namespace is dumped and something fails, sockets
remain in repair mode. It's because cpt_unlock_tcp_connections is
executed only if network namespace is not dumped.

cpt_unlock_tcp_connections disables repair mode for sockets and drops
netfilters. netfilters are not used in case of network namespaces.

v2: don't execute network-unlock scripts, if network namespace are not
    dumped.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>