[FIX] Fix get_default_ method decorator and definition

In sale.config.settings, the method get_default_sale_config has api.multi decorator.
However, the method definition should be def get_default_sale_config(self, cr, uid, fields, context)
(see https://github.com/odoo/odoo/blob/9.0/openerp/addons/base/res/res_config.py#L534 ).
The api.multi decorator results in the model being browsed with fields as ids, which results in that kind of queries:

select * from sale_config_settings where id in ('generate_sales_team_alias')

This change corrects the method definition to fix that.

addons/sale_stock/res_config.py

@@ -28,8 +28,8 @@ class SaleConfiguration(models.TransientModel):
         ], "Order Routing",
         implied_group='sale_stock.group_route_so_lines')
 
-    @api.multi
-    def get_default_sale_config(self):
+    @api.model
+    def get_default_sale_config(self, fields):
         default_picking_policy = self.env['ir.values'].get_default('sale.order', 'picking_policy')
         return {
             'default_picking_policy': 1 if default_picking_policy == 'one' else 0,