Use c program as the eBPF kernel program

With proper Clang and LLVM support. The eBPF program can be compiled and
generated from simplified C program. The original c program is
bpf_ingress.c and bpf_egress.c and the corresponding .o file the output
containing the BPF bytecode that need to be loaded into the kernel at
runtime.

Bug: 30950746
Test: run cts -m CtsNetTestCases -t android.net.cts.TrafficStatsTest
Change-Id: Iedff82bf759c979bbe8e698570eabba436b56d80