Bug fix of Tx PER when packet count is low

Use default Tx PER when packet count is low because PER estimation is
unreliable with low Tx packet count.

Bug: 159866355
Test: atest com.android.server.wifi
Change-Id: Ide48ab41420c9c907fc50a32aef10b47360209d4
3 files changed
tree: e98851bf99c5dcdfc080c4cbd84414c8aa2920cc
  1. apex/
  2. service/
  3. metrics_pdd_hook.py
  4. PREUPLOAD.cfg