Simplify the traffic stats entry struct

Since the framework API no longer support traffic stats detail such as
rxTcpPacket number or rxTcpBytes, The eBPF program and the native helper
functions no longer need to store those information as well. Removing
them from the struct StatsValue can save some space per stats entry and
reduce the total size of stats map.

Bug: 30950746
Test: run cts -m CtsNetTestCases -t android.net.cts.TrafficStatsTest
Change-Id: I70c24b762ecc9d58fc4a3ac48a7944416eff7c81