eth/catalyst: fix NewPayload warn log when dropping due to snap sync

eth/catalyst/api.go

@@ -417,7 +417,17 @@ func (api *ConsensusAPI) delayPayloadImport(block *types.Block) (beacon.PayloadS
 	// payload as non-integratable on top of the existing sync. We'll just
 	// have to rely on the beacon client to forcefully update the head with
 	// a forkchoice update request.
-	log.Warn("Ignoring payload with missing parent", "number", block.NumberU64(), "hash", block.Hash(), "parent", block.ParentHash())
+	if api.eth.SyncMode() == downloader.FullSync {
+		// In full sync mode, failure to import a well-formed block can only mean
+		// that the parent state is missing and the syncer rejected extending the
+		// current cycle with the new payload.
+		log.Warn("Ignoring payload with missing parent", "number", block.NumberU64(), "hash", block.Hash(), "parent", block.ParentHash())
+	} else {
+		// In non-full sync mode (i.e. snap sync) all payloads are rejected until
+		// snap sync terminates as snap sync relies on direct database injections
+		// and cannot afford concurrent out-if-band modifications via imports.
+		log.Warn("Ignoring payload while snap syncing", "number", block.NumberU64(), "hash", block.Hash())
+	}
 	return beacon.PayloadStatusV1{Status: beacon.ACCEPTED}, nil
 }