Fix effective gas price calculation (#2303)

6351612 introduced the bug by
accidentally losing the negation in `if
!s.b.ChainConfig().IsLondon(bigblock)`. This results in wrong
`effectiveGasPrice` values to be returned from the RPC. The actually
transferred fees are correct.

internal/ethapi/api.go

@@ -2135,7 +2135,7 @@ func generateReceiptResponse(ctx context.Context, backend Backend, receipt *type
 		fields["from"], _ = types.Sender(signer, tx)
 		fields["to"] = tx.To()
 		// Assign the effective gas price paid
-		if backend.ChainConfig().IsLondon(new(big.Int).SetUint64(blockNumber)) {
+		if !backend.ChainConfig().IsLondon(new(big.Int).SetUint64(blockNumber)) {
 			fields["effectiveGasPrice"] = hexutil.Uint64(tx.GasPrice().Uint64())
 		} else {
 			// var gasPrice *big.Int = new(big.Int)