Don't check qtaguid file unless using them

The proc file of xt_qtaguid module is not necessarily exist on future
devices. We should only check it if the device need to read the stats
file for network usage information.

Bug: 79938294
Test: NetworkUsageStatsTest TrafficStatsTest
Change-Id: I5ac6feef8b9a26daa68b381a985925e24b0d80af