Evict inactive peers from the collator protocol peer-set (#2680)

* malicious reputation cost is fatal

* make ReportBad a malicious cost

* futures control-flow for cleaning up inactive collator peers

* guide: network bridge updates

* add `PeerDisconnected` message

* guide: update

* reverse order

* remember to match

* implement disconnect peer in network bridge

* implement disconnect_inactive_peers

* test

* remove println

* don't hardcore policy

* add fuse outside of loop

* use default eviction policy

polkadot/roadmap/implementers-guide/src/node/utility/network-bridge.md

@@ -86,6 +86,10 @@ Map the message onto the corresponding [Event Handler](#event-handlers) based on
 
 - Adjust peer reputation according to cost or benefit provided
 
+### DisconnectPeer
+
+- Disconnect the peer from the peer-set requested, if connected.
+
 ### SendValidationMessage / SendValidationMessages
 
 - Issue a corresponding `ProtocolMessage` to each listed peer on the validation peer-set.

polkadot/roadmap/implementers-guide/src/types/overseer-protocol.md

@@ -328,7 +328,9 @@ enum PeerSet {
 
 enum NetworkBridgeMessage {
     /// Report a cost or benefit of a peer. Negative values are costs, positive are benefits.
-    ReportPeer(PeerSet, PeerId, cost_benefit: i32),
+    ReportPeer(PeerId, cost_benefit: i32),
+    /// Disconnect a peer from the given peer-set without affecting their reputation.
+    DisconnectPeer(PeerId, PeerSet),
     /// Send a message to one or more peers on the validation peerset.
     SendValidationMessage([PeerId], ValidationProtocolV1),
     /// Send a message to one or more peers on the collation peerset.