[SP28] Add API for set data warning

To have better control and race-free of set data warning
to tether offload hardware, an interface of set warning and
limit at the same time in the NetworkStatsProvider is needed.

This is a no-op change which expose such interface with minimum
changes in service side to get build pass. The implementation
would be included in follow-up patches.

Test: atest NetworkStatsServiceTest
Test: atest NetworkPolicyManagerServiceTest
Test: atest GtsNetworkStackHostTestCases
Test: m doc-comment-check-docs
Bug: 149467454
Bug: 170699770
Bug: 170179169
Ignore-AOSP-First: avoid long automerger delay
Change-Id: I6ee661497f7dedb871c85786d1950cab951d8aa2