Max size of attachment is not correctly detected (Forum and Assignment)

This issue only needs to be tested in one device.

1.  In web as admin/teacher, create a course with a certain "Maximum upload size" (e.g. 10MB).
2. In this course, create 2 forums: 
   1. The first one (F1) with "Maximum attachment size" set to "Course upload limit".
   2. The second one (F2) with "Maximum attachment size" set to a lower size, e.g. 5MB.
3. In another course with "Maximum upload size" set to "Site upload limit", create a forum (F3) with "Maximum attachment size" set to "Site upload limit".
4. In the app, login as a student.
5. Open forum F1 and click to add a new discussion. Check that in the attachments part the right size is displayed (it should match the course limit) and the app doesn't allow adding files bigger than that size.
6. Now open forum F2 and click to add a new discussion. Check that in the attachments part the right size is displayed (it should match the custom size set) and the app doesn't allow adding files bigger than that size.
7. Now open forum F3 and click to add a new discussion. Check that in the attachments part the right size is displayed (it should match the site upload limit) and the app doesn't allow adding files bigger than that size.
8. Optional: you can repeat this test using other activities that allow attachments in the app: assign, database, glossary, quiz (essay), workshop. The code is the same for all activities so IMO this test is optional.