refactor bpf kernel program

Refactor the program into several inline function and resolve the
duplication of ingress program and egress program. The Program compiled
from the new inline function should be no difference compare to the old
ones.

Bug: 30950746
Test: bpf program can be loaded.
      atest android.net.cts.TrafficStatsTest
      atest android.app.usage.cts.NetworkUsageStatsTest
Change-Id: I8091e8bdf7f3fe118c26907028e3f845eb41ab65