Further headset mode robustification based on linear filter convergence

This CL adds robustifications for avoiding that the headset mode
is triggered for reverberant or weak echo paths.

Bug: webrtc:9047,chromium:824111,webrtc:8314,webrtc:8671,webrtc:5201,webrtc:5919
Change-Id: Ib111e617f765377c021a5b633cf13a7917fe62a6
Reviewed-on: https://webrtc-review.googlesource.com/64002
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Commit-Queue: Per Åhgren <peah@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22557}

modules/audio_processing/aec3/aec_state.h

@@ -173,6 +173,8 @@ class AecState {
   bool converged_filter_seen_ = false;
   bool consistent_filter_seen_ = false;
   bool external_delay_seen_ = false;
+  size_t converged_filter_count_ = 0;
+  bool finite_erl_ = false;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(AecState);
 };