Add operation counts to network statistics.

Provide API to increment "operation counts" for a UID and tag, used
to eventually derive bytes/operation stats.  Internally is stored at
network layer, but should belong at data layer.  Switch profiling
to use data layer stats, which are emulated by summarizing network
layer details.

Read packet counts from new /proc/ columns and collect them into
NetworkStatsHistory.  Prevent double-counting by ignoring values from
first snapshot.  Watch for duplicate /proc/ entries.  Update tests
to verify packet and operation counters.

Bug: 5052136, 5097392
Change-Id: I1832f65a2b8a9188f8088f253474a667c21a2f09