Implement `sort.Interface` interface on `AddressGroup` and perform sorting
in `AddressGroup.FromIterator` method. Addresses with enabled TLS are "less"
in terms of slice position.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Define `network.AddressGroup` type which represents group of network
addresses. This type is going to be used to support group-address of the
storage node.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
