params: postpone Constantinople due to net SSTORE reentrancy

params/config.go

@@ -42,7 +42,7 @@ var (
 		EIP155Block:         big.NewInt(2675000),
 		EIP158Block:         big.NewInt(2675000),
 		ByzantiumBlock:      big.NewInt(4370000),
-		ConstantinopleBlock: big.NewInt(7080000),
+		ConstantinopleBlock: nil,
 		Ethash:              new(EthashConfig),
 	}