Fix clang style warnings in webrtc/modules/audio_coding/neteq

Mostly this consists of marking functions with override when
applicable, and moving function bodies from .h to .cc files.

BUG=163
R=henrik.lundin@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44109004

Cr-Commit-Position: refs/heads/master@{#8960}

webrtc/modules/audio_coding/neteq/timestamp_scaler.h

@@ -36,7 +36,7 @@ class TimestampScaler {
   virtual ~TimestampScaler() {}
 
   // Start over.
-  virtual void Reset() { first_packet_received_ = false; }
+  virtual void Reset();
 
   // Scale the timestamp in |packet| from external to internal.
   virtual void ToInternal(Packet* packet);