After recent changes Netmap contract can send `UpdateState` notification
event with `MAINTENANCE` node's state. There is a need to provide
functionality to work with the status.
Provide `UpdatePeer.Maintenance` method. Support new state in
`ParseUpdatePeer` and `ParseUpdatePeerNotary` functions.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
New network status of storage nodes is going to be introduced. To
simplify the addition, it would be useful to prepare the code for this.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
