If the qtaguid proc file is no longer exist, the device is running new
eBPF module to do traffic accounting. So the NetworkStatsFactory need to
use the proc/net/dev interface to get the per interface traffic stats
summary. Also, adding a test to verify the helper function work properly
Bug: 30950746
Test: run NetworkStatsFactoryTest
Change-Id: Ia36808bf02f1637dd41a3e7c50917b91b1a77524
b25ada3657