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.cc

@@ -16,6 +16,10 @@
 
 namespace webrtc {
 
+void TimestampScaler::Reset() {
+  first_packet_received_ = false;
+}
+
 void TimestampScaler::ToInternal(Packet* packet) {
   if (!packet) {
     return;