discovery: implement ChannelAnnouncement banning

This commit hooks up the banman to the gossiper:
- peers that are banned and don't have a channel with us will get
  disconnected until they are unbanned.
- peers that are banned and have a channel with us won't get
  disconnected, but we will ignore their channel announcements until
  they are no longer banned. Note that this only disables gossip of
  announcements to us and still allows us to open channels to them.

server.go

@@ -1026,6 +1026,8 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		return nil, err
 	}
 
+	scidCloserMan := discovery.NewScidCloserMan(s.graphDB, s.chanStateDB)
+
 	s.authGossiper = discovery.New(discovery.Config{
 		Graph:                 s.graphBuilder,
 		Notifier:              s.cc.ChainNotifier,
@@ -1063,6 +1065,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		GetAlias:                s.aliasMgr.GetPeerAlias,
 		FindChannel:             s.findChannel,
 		IsStillZombieChannel:    s.graphBuilder.IsZombieChannel,
+		ScidCloser:              scidCloserMan,
 	}, nodeKeyDesc)
 
 	//nolint:lll
@@ -3639,11 +3642,34 @@ func (s *server) InboundPeerConnected(conn net.Conn) {
 	}
 
 	nodePub := conn.(*brontide.Conn).RemotePub()
-	pubStr := string(nodePub.SerializeCompressed())
+	pubSer := nodePub.SerializeCompressed()
+	pubStr := string(pubSer)
+
+	var pubBytes [33]byte
+	copy(pubBytes[:], pubSer)
 
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
+	// If the remote node's public key is banned, drop the connection.
+	shouldDc, dcErr := s.authGossiper.ShouldDisconnect(nodePub)
+	if dcErr != nil {
+		srvrLog.Errorf("Unable to check if we should disconnect "+
+			"peer: %v", dcErr)
+		conn.Close()
+
+		return
+	}
+
+	if shouldDc {
+		srvrLog.Debugf("Dropping connection for %v since they are "+
+			"banned.", pubSer)
+
+		conn.Close()
+
+		return
+	}
+
 	// If we already have an outbound connection to this peer, then ignore
 	// this new connection.
 	if p, ok := s.outboundPeers[pubStr]; ok {
@@ -3726,11 +3752,38 @@ func (s *server) OutboundPeerConnected(connReq *connmgr.ConnReq, conn net.Conn)
 	}
 
 	nodePub := conn.(*brontide.Conn).RemotePub()
-	pubStr := string(nodePub.SerializeCompressed())
+	pubSer := nodePub.SerializeCompressed()
+	pubStr := string(pubSer)
+
+	var pubBytes [33]byte
+	copy(pubBytes[:], pubSer)
 
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
+	// If the remote node's public key is banned, drop the connection.
+	shouldDc, dcErr := s.authGossiper.ShouldDisconnect(nodePub)
+	if dcErr != nil {
+		srvrLog.Errorf("Unable to check if we should disconnect "+
+			"peer: %v", dcErr)
+		conn.Close()
+
+		return
+	}
+
+	if shouldDc {
+		srvrLog.Debugf("Dropping connection for %v since they are "+
+			"banned.", pubSer)
+
+		if connReq != nil {
+			s.connMgr.Remove(connReq.ID())
+		}
+
+		conn.Close()
+
+		return
+	}
+
 	// If we already have an inbound connection to this peer, then ignore
 	// this new connection.
 	if p, ok := s.inboundPeers[pubStr]; ok {