Add NetworkTraceHandler with Start/Stop/ConsumeAll

This adds the base (non-perfetto) NetworkTraceHandler with support for
starting and stopping tracing, and pulling messages from BPF. The
included test covers the end-to-end scenario from socket creation,
socket tagging and data traffic.

Bug: 246985031
Test: atest --iterations 500 libnetworkstats_test
Change-Id: I035d2e03fa7c461ecb93d207b7fd2f53e6a2f52e
4 files changed