Update the comment about tag limit

describe more details about the total uid stats entries limit in the
definition to make it better to understand.

Bug: 126620214
Test: Build
Change-Id: Ic2cdbc7cff7b8fa41316d9193c3eaf70536296c9
Merged-In: Ic2cdbc7cff7b8fa41316d9193c3eaf70536296c9
(cherry picked from commit 05662bef)