[FIX] mass_mailing_sms : the sms_allow_unsubscribe field invisible for mailing marketing

The field sms_allow_unsubscribe field was visible and checkable on the
email marketing app, but this field is reserved to the
sms marketing. Add a invisible condition.

TASK_ID : 2078918

addons/mass_mailing_sms/views/mailing_mailing_views.xml

@@ -110,7 +110,7 @@
                 </page>
             </xpath>
             <xpath expr="//field[@name='user_id']" position="after">
-                <field name="sms_allow_unsubscribe"/>
+                <field name="sms_allow_unsubscribe" attrs="{'invisible': [('mailing_type', '!=', 'sms')]}"/>
             </xpath>
             <!-- Option page tweaks -->
             <xpath expr="//field[@name='email_from']" position="attributes">