[FIX] base: set vat number field as readonly on children partners; as it is a...

[FIX] base: set vat number field as readonly on children partners; as it is a commercial field, it should always have the value defined on the parent partner.

(this is a manual forward port from https://github.com/odoo/odoo/commit/98b1fffd4e99cc8ad2862c56fbd727979c38c48b , as a new view is defined in 11.0, needing this correction too)

odoo/addons/base/res/res_partner_view.xml

@@ -171,7 +171,7 @@
                                 <field name="country_id" placeholder="Country" class="o_address_country" options='{"no_open": True, "no_create": True}'
                                     attrs="{'readonly': [('type', '=', 'contact'),('parent_id', '!=', False)]}"/>
                             </div>
-                            <field name="vat" placeholder="e.g. BE0477472701"/>
+                            <field name="vat" placeholder="e.g. BE0477472701" attrs="{'readonly': [('parent_id','!=',False)]}"/>
                         </group>
                         <group>
                             <field name="function" placeholder="e.g. Sales Director"
@@ -244,7 +244,7 @@
                                 <field name="country_id" placeholder="Country" class="o_address_country" options='{"no_open": True, "no_create": True}'
                                     attrs="{'readonly': [('type', '=', 'contact'),('parent_id', '!=', False)]}"/>
                             </div>
-                            <field name="vat" placeholder="e.g. BE0477472701"/>
+                            <field name="vat" placeholder="e.g. BE0477472701" attrs="{'readonly': [('parent_id','!=',False)]}"/>
                             <field name="category_id" widget="many2many_tags" options="{'color_field': 'color', 'no_create_edit': True}" placeholder="Tags..."/>
                         </group>
                         <group>