ACM/NetEq: Restructure how post-decode VAD is enabled

webrtc/modules/audio_coding/neteq/neteq_impl.cc

Index: webrtc/modules/audio_coding/neteq/neteq_impl.cc
diff --git a/webrtc/modules/audio_coding/neteq/neteq_impl.cc b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
index ecd1ad9fabe7971312309928aae015b7f43bfb5b..18d67c45f22a3bdafcf1ac6815d98fcf8bd9cb37 100644
--- a/webrtc/modules/audio_coding/neteq/neteq_impl.cc
+++ b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
@@ -112,6 +112,10 @@ NetEqImpl::NetEqImpl(const NetEq::Config& config,
   if (create_components) {
     SetSampleRateAndChannels(fs, 1);  // Default is 1 channel.
   }
+  RTC_DCHECK(!vad_->enabled());
+  if (config.enable_post_decode_vad) {
+    vad_->Enable();
+  }
 }
 
 NetEqImpl::~NetEqImpl() = default;