Always splice historical data stats, debug info.

When reading network counters, always splice in xt_qtaguid values
to avoid counting backwards. Test to verify.

Remove verbose logging around global alerts, and add dumpsys debug
info for NMS and MDST. Also fix subtle bug around stats persisting
and dumping.

Bug: 5212893, 5211028
Change-Id: I783e5286637a67ee2dd2b09878198711a926d0cb