Advanced settings discussion category ids should be unique.

If the ids in the adnvaced setting discussion category are
not unique then threads under categories with different name
will come in every category with same id. Ids should be unique
inorder to differentiate between different categories.

TNL-752
Merge pull request #5993 from mlkwaqas/waqas/tnl752-discussion-id-should-be-unique

Advanced settings discussion category ids should be unique.