[opus] Apply patch to fix off-by-one issue in Silk DTX

https://github.com/xiph/opus/pull/73

Bug: webrtc:8088
Change-Id: Ie3838e5c8600259af46bdf09680e58dcf55f78a2
Reviewed-on: https://chromium-review.googlesource.com/942317Reviewed-by: Henrik Andreasson <henrika@chromium.org>
Commit-Queue: Felicia Lim <flim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540976}

third_party/opus/README.chromium

@@ -15,3 +15,4 @@ Local changes:
 * copy .gitignore from https://git.xiph.org/?p=opus.git;a=tree
 * set 'x' flags: "chmod 750 win32/genversion.bat"
 * Apply https://git.xiph.org/?p=opus.git;a=commitdiff;h=46560534fcb5710a894a341c2f9526db58fd7087#patch1
+* Apply https://github.com/xiph/opus/pull/73

third_party/opus/src/silk/fixed/encode_frame_FIX.c

@@ -57,7 +57,7 @@ void silk_encode_do_VAD_FIX(
     if( psEnc->sCmn.speech_activity_Q8 < SILK_FIX_CONST( SPEECH_ACTIVITY_DTX_THRES, 8 ) ) {
         psEnc->sCmn.indices.signalType = TYPE_NO_VOICE_ACTIVITY;
         psEnc->sCmn.noSpeechCounter++;
-        if( psEnc->sCmn.noSpeechCounter < NB_SPEECH_FRAMES_BEFORE_DTX ) {
+        if( psEnc->sCmn.noSpeechCounter <= NB_SPEECH_FRAMES_BEFORE_DTX ) {
             psEnc->sCmn.inDTX = 0;
         } else if( psEnc->sCmn.noSpeechCounter > MAX_CONSECUTIVE_DTX + NB_SPEECH_FRAMES_BEFORE_DTX ) {
             psEnc->sCmn.noSpeechCounter = NB_SPEECH_FRAMES_BEFORE_DTX;

third_party/opus/src/silk/float/encode_frame_FLP.c

@@ -56,7 +56,7 @@ void silk_encode_do_VAD_FLP(
     if( psEnc->sCmn.speech_activity_Q8 < SILK_FIX_CONST( SPEECH_ACTIVITY_DTX_THRES, 8 ) ) {
         psEnc->sCmn.indices.signalType = TYPE_NO_VOICE_ACTIVITY;
         psEnc->sCmn.noSpeechCounter++;
-        if( psEnc->sCmn.noSpeechCounter < NB_SPEECH_FRAMES_BEFORE_DTX ) {
+        if( psEnc->sCmn.noSpeechCounter <= NB_SPEECH_FRAMES_BEFORE_DTX ) {
             psEnc->sCmn.inDTX = 0;
         } else if( psEnc->sCmn.noSpeechCounter > MAX_CONSECUTIVE_DTX + NB_SPEECH_FRAMES_BEFORE_DTX ) {
             psEnc->sCmn.noSpeechCounter = NB_SPEECH_FRAMES_BEFORE_DTX;