les: limit LES peer count and improve peer configuration logic (#16010)

* les: limit number of LES connections

* eth, cmd/utils: light vs max peer configuration logic

les/helper_test.go

@@ -176,7 +176,7 @@ func newTestProtocolManager(lightSync bool, blocks int, generator func(int, *cor
 		srv.fcManager = flowcontrol.NewClientManager(50, 10, 1000000000)
 		srv.fcCostStats = newCostStats(nil)
 	}
-	pm.Start()
+	pm.Start(1000)
 	return pm, nil
 }