les: log disconnect reason when light server is not synced (#20643)

Co-authored-by: ligi <ligi@ligi.de>

les/server_handler.go

@@ -128,6 +128,7 @@ func (h *serverHandler) handle(p *peer) error {
 	}
 	// Reject light clients if server is not synced.
 	if !h.synced() {
+		p.Log().Debug("Light server not synced, rejecting peer")
 		return p2p.DiscRequested
 	}
 	defer p.fcClient.Disconnect()