Add the native implementation for NetworkStatsService to read the
uidStatsMap and tagStatsMap to get the network traffic information.
Currently the implementation only try to get the data from bpf for a
reference but the final value returned is still from old xt_qtaguid
module. So the result will not be effected. The bpf implementation is
depending on libbpf inside netd.
Bug: 30950746
Test: CtsNetTestCases -t android.net.cts.TrafficStatsTest
Change-Id: Ia85e4d4d602f6bd536739d89085e6dc37ad82e15
7d2d414fd8