Skip DNS event if dns data stall detection is disabled

Data stall detection using DNS event can be controlled by
DeviceConfig. However, feature disable only skip data stall
evaluation. DNS events are still processed. Update to disable
all events handle if feature is disabled.

Bug: 147857311
Test: atest NetworkStackTests
Test: Test with ./out/host/linux-x86/bin/statsd_testdrive 121
      to ensure log properly

Change-Id: I985af202d4406b831dbf3d66bcae14794f3ca26d