Limit data usage request per uid

Currently, there is no limtation for an app to request
data usage callback, which is dangerous if the app fire
hundreds of thousands requests and potientially this might
cause OOM if the apps don't free them.

Test: atest NetworkStatsObserversTest#testRegister_limit
Bug: 229103088
Change-Id: I8299f46fd47a82ec9b25ba2e0d3c95db5512c331
3 files changed