Sort and group network stats collected from eBPF.

Since eBPF use hash map to record stats, network stats collected
from eBPF will be out of order. And the performance of
findIndexHinted in NetworkStats would be impacted.

Furthermore, since the StatsKey contains iface index, the
network stats reported to framework would create items with the
same iface, uid, tag and set, which causes NetworkStats maps
wrong item to subtract.

Thus, the stats needs to be properly sorted and grouped before
reported.

Bug: 112226716
Bug: 119193941
Test: 1. manually reconnect vpn
      2. update apps from playstore
      3. atest libbpf_test
      4. runtest frameworks-net
      5. cts-tradefed run cts -m CtsUsageStatsTestCases -t \
              android.app.usage.cts.NetworkUsageStatsTest

Change-Id: I7cb622bfcc643f6e1a0ab59c5aafa85319313493
Merged-In: I6d485a368fd8e52d21d5e894fc189ac8f0e9f502