[SM03] Collect NetworkStats metrics by NetworkTemplate

This is a no-op refactoring prior to follow-up patches which
will collect NetworkStats from history based on specified template.

Test: adb shell cmd stats pull-source 10000~10003
      adb shell dumpsys netstats --uid
      atest HostAtomTests
Bug: 129082217

Change-Id: I64f0866fee078aa8b246c527c3c1196c8380783f