Move kernelToTag to NetworkStatsFactory. am: 09d2a4b175 am: b9e2b370fb am: d967a2faa0 am: 7667882f9f

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1964913

Change-Id: I0d7a250e321ff80dc4ab94c57c6fb9ea7c793677