internal/ethapi: refactor TxArgs.setCancunFeeDefaults (ethereum#30541)

calculating a reasonable tx blob fee cap (`max_blob_fee_per_gas *
total_blob_gas`) only depends on the excess blob gas of the parent
header. The parent header is assumed to be correct, so the method should
not be able to fail and return an error.

internal/ethapi/transaction_args.go

@@ -189,9 +189,7 @@ func (args *TransactionArgs) setFeeDefaults(ctx context.Context, b Backend) erro
 	if args.BlobFeeCap != nil && args.BlobFeeCap.ToInt().Sign() == 0 {
 		return errors.New("maxFeePerBlobGas, if specified, must be non-zero")
 	}
-	if err := args.setCancunFeeDefaults(ctx, head, b); err != nil {
-		return err
-	}
+	args.setCancunFeeDefaults(head)
 	// If both gasPrice and at least one of the EIP-1559 fee parameters are specified, error.
 	if args.GasPrice != nil && (args.MaxFeePerGas != nil || args.MaxPriorityFeePerGas != nil) {
 		return errors.New("both gasPrice and (maxFeePerGas or maxPriorityFeePerGas) specified")
@@ -243,7 +241,7 @@ func (args *TransactionArgs) setFeeDefaults(ctx context.Context, b Backend) erro
 }
 
 // setCancunFeeDefaults fills in reasonable default fee values for unspecified fields.
-func (args *TransactionArgs) setCancunFeeDefaults(ctx context.Context, head *types.Header, b Backend) error {
+func (args *TransactionArgs) setCancunFeeDefaults(head *types.Header) {
 	// Set maxFeePerBlobGas if it is missing.
 	if args.BlobHashes != nil && args.BlobFeeCap == nil {
 		var excessBlobGas uint64
@@ -258,7 +256,6 @@ func (args *TransactionArgs) setCancunFeeDefaults(ctx context.Context, head *typ
 		val := new(big.Int).Mul(blobBaseFee, big.NewInt(2))
 		args.BlobFeeCap = (*hexutil.Big)(val)
 	}
-	return nil
 }
 
 // setLondonFeeDefaults fills in reasonable default fee values for unspecified fields.