Impacted versions: 9.0

Steps to reproduce:

* Create an MTO product with 
  * Product Type: Stockable Product
  * Routes: "Buy" and "Make to Order"
* Update Qty on Hand to any quantity (i.e, 2).
* Create a sales order with this product and a number <= to the one in the step before.
* Confirm the sales order.

Current behavior:

The created delivery picking appears in state "Reserved" and the current quantity on stock has been reserved, allowing you to transfer that stock.

Expected behavior:

The created delivery picking should be in "Waiting another operation", or at least in "Waiting availability" until the purchase order is confirmed (if you have defined a supplier for the product and the procurement creates the purchase order), which seems to be the current behavior when there's no stock available (is this also correct, as it allows to manually reserve?).
addons/stock/stock.py
stock_pack_operation_obj = self.pool.get('stock.pack.operation')
        if default is None:
            default = {}
        new_package_id = self.copy(cr, uid, id, default_pack_values, context=context)
        default['result_package_id'] = new_package_id
        op_ids = stock_pack_operation_obj.search(cr, uid, [('result_package_id', '=', id)], context=context)
        for op_id in op_ids:
            stock_pack_operation_obj.copy(cr, uid, op_id, default, context=context)
class stock_pack_operation(osv.osv):
    _name = "stock.pack.operation"
    _description = "Packing Operation"
    _order = "result_package_id desc, id"
    def _get_remaining_prod_quantities(self, cr, uid, operation, context=None):
        '''Get the remaining quantities per product on an operation with a package. This function returns a dictionary'''
        
        if not operation.package_id or operation.product_id:
            return {operation.product_id: operation.remaining_qty}
        
        res = self.pool.get('stock.quant.package')._get_all_products_quantities(cr, uid, operation.package_id.id, context=context)
        
        for record in operation.linked_move_operation_ids:
            if record.move_id.product_id.id not in res:
                res[record.move_id.product_id] = 0
            res[record.move_id.product_id] -= record.qty
        return res
    def _get_remaining_qty(self, cr, uid, ids, name, args, context=None):