Use bpf map to read the interface stats

With the support of xt_bpf module, the more accurate per interface
network traffic stats can be obtained from ifaceStatsMap under
sys/fs/bpf/. Change the framework NetworkStatsService native
implementation to read from map instead of /proc/net/dev. The
corresponding test is added and refactor the old test to be compatible.

Test: ./libbpf_test
      atest android.net.cts.TrafficStatsTest
Bug: 72111305

Change-Id: I2a6c6f82317bd9667c1b15e6b082fc9f153f6bf3