Add unit test cases for TrafficController

The unit test cases use fake eBPF map to verify the behavior of
TrafficController API such as tag/untag socket and set counter set.
It use four temperary bpf maps to store the result of
TrafficController.

Bug: 30950746
Test: run netd_unit_test
Change-Id: I71ad301475034986ca403a87b81b0cbfc354ae18
6 files changed