Track xtables summary, move tether stats, time.

Begin tracking xtables summary of data usage to compare with values
reported from /proc/net/dev.  Roll tethering directly into UID stats
to trigger UID stats persisting when crossing threshold.

Include xtables summary and authoritative time in samples.

Bug: 5373561, 5397882, 5381980
Change-Id: Ib7945522caadfbe0864fdf391582dc820f4f371e
6 files changed