Fine tune the IntelligibilityEnhancer

Label less chunks as speech, adapt slower and be more conservative with the maximum gain it can apply.

Review-Url: https://codereview.webrtc.org/2087623003
Cr-Original-Commit-Position: refs/heads/master@{#13242}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 7bd5f253bc09fe18bc4190fe88dbba9792ce32ae
3 files changed