discovery+server: add more trace log

discovery/gossiper.go

@@ -1293,7 +1293,8 @@ func (d *AuthenticatedGossiper) sendRemoteBatch(annBatch []msgWithSenders) {
 
 	// We'll first attempt to filter out this new message for all peers
 	// that have active gossip syncers active.
-	for _, syncer := range syncerPeers {
+	for pub, syncer := range syncerPeers {
+		log.Tracef("Sending messages batch to GossipSyncer(%x)", pub)
 		syncer.FilterGossipMsgs(annBatch...)
 	}
 

discovery/syncer.go

@@ -1251,6 +1251,8 @@ func (g *GossipSyncer) FilterGossipMsgs(msgs ...msgWithSenders) {
 	// If the peer doesn't have an update horizon set, then we won't send
 	// it any new update messages.
 	if g.remoteUpdateHorizon == nil {
+		log.Tracef("GossipSyncer(%x): skipped due to nil "+
+			"remoteUpdateHorizon", g.cfg.peerPub[:])
 		return
 	}