Wifi usability: Data stall detection based on link layer stats

This is an effort to define new criterion for triggering Wifi data stall:
(1) Defined data stall criterion based on transmit and/or receive throughput, transmit packet error rate, and CCA level. Data stall is triggered when transmit and/or receive links are consecutively bad over multiple RSSI polls.
(2) Added DeviceConfig flags (that is disabled by default) which may be configured on the server side to tune the thresholds at which data stall gets triggered.

Bug: 141027476
Test: frameworks/base/wifi/tests/runtests.sh

Change-Id: I895fd54cc7ec32815bce1899354ca265d4e93ea9
Signed-off-by: Mingguang Xu <mingguangxu@google.com>
Merged-In: I76d6338cd2d482d198fde1e5a2d1a0540c087ca6