les, core/bloombits: post-LES/2 fixes (#15391)

* les: fix topic ID

* core/bloombits: fix interface conversion

core/bloombits/matcher.go

@@ -534,7 +534,10 @@ func (s *MatcherSession) Close() {
 
 // Error returns any failure encountered during the matching session.
 func (s *MatcherSession) Error() error {
-	return s.err.Load().(error)
+	if err := s.err.Load(); err != nil {
+		return err.(error)
+	}
+	return nil
 }
 
 // AllocateRetrieval assigns a bloom bit index to a client process that can either

les/backend.go

@@ -145,7 +145,7 @@ func lesTopic(genesisHash common.Hash, protocolVersion uint) discv5.Topic {
 	default:
 		panic(nil)
 	}
-	return discv5.Topic(name + common.Bytes2Hex(genesisHash.Bytes()[0:8]))
+	return discv5.Topic(name + "@" + common.Bytes2Hex(genesisHash.Bytes()[0:8]))
 }
 
 type LightDummyAPI struct{}