[SP29] Send interface warning bytes to NetworkStatsProvider

This change contains necessary modification in NPMS and NSS
to send warning bytes to NetworkStatsProvider. But since
no any provider has been upgraded to handle such parameter.
Thus, no behavior change is made in this patch.

Test: atest NetworkPolicyManagerServiceTest NetworkStatsServiceTest
Test: atest NetworkPolicyManagerServiceTest#testStatsProviderWarningAndLimitReached
Bug: 149467454
Bug: 170699770
Bug: 170179169
Ignore-AOSP-First: avoid long automerger delay
Change-Id: I6c4863030c36328db571294fd12a40e59864def5