sockets: Restore unconnected dgram sockets v7

In case if dgram socket peer is not connected back
we can try to resolve peer by name.

For security reason this happens only if '-x' option
is passed at checkpoint and restore time.

In particular this is needed for programs which do
use dgram socket to send messages to /dev/log.

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