AGC2 adaptive digital false by default

Avoid that the client code relies on the adaptive digital mode being
enabled by default (error prone).

Bug: webrtc:7494
Change-Id: I765fecf535cf31a2163e10595a42520473c233b6
Reviewed-on: https://webrtc-review.googlesource.com/c/111586
Reviewed-by: Alex Loiko <aleloi@webrtc.org>
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25728}

modules/audio_processing/include/audio_processing.h

diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index 5467a38..9a1a03c 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -276,7 +276,7 @@
         float gain_db = 0.f;
       } fixed_digital;
       struct {
-        bool enabled = true;
+        bool enabled = false;
         LevelEstimator level_estimator = kRms;
         bool use_saturation_protector = true;
         float extra_saturation_margin_db = 2.f;