use the alias object directly

The alias object returns its email address when it's called as a string.
Therefor it's better to call the object directly.

network_inventory/inventory/templates/inventory/user_details.html

@@ -52,7 +52,7 @@
     {% for alias in mail_alias %}
     <tr>
     <td>
-    {{ alias.email_address }}
+    {{ alias }}
     </td>
     </tr>
     {% endfor %}