Avoid excessive allocation churn in network stats.

Getting the network stats required making 3 full copies of all the
network stats since boot. Reorganize the code so we only have to
allocate incremental network stats objects.

Flag: EXEMPT bugfix
Bug: 399154099
Test: atest ConnectivityCoverageTests
Test: atest NetworkStatsIntegrationTest
Change-Id: Id531c4ffd6e0d127b8aaac38bda6a89a3d700c64
2 files changed