Use a separate map to store per app stats

To avoid iterating through the eBPF map to get the total stats of a
specific uid. A new bpf map called appUidStatsMap is added to the
trafficController so that TrafficStats API can directly read that map
for per uid total stats regardless of tag, counterSet and iface
information. This could make this call more efficient and solve the
possible racing problem.

Bug: 79171384
Test: netd_unit_test, libbpf_test, netd_integration_test
Change-Id: I47a4ac3466caa729c5730a498a2de226303d6b77
Merged-In: I47a4ac3466caa729c5730a498a2de226303d6b77
(cherry picked from aosp commit bc4a15f9)