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}
diff --git a/webrtc/modules/audio_coding/neteq/neteq_impl.h b/webrtc/modules/audio_coding/neteq/neteq_impl.h
index ac4689b..76b23e3 100644
--- a/webrtc/modules/audio_coding/neteq/neteq_impl.h
+++ b/webrtc/modules/audio_coding/neteq/neteq_impl.h
@@ -73,7 +73,7 @@
             PreemptiveExpandFactory* preemptive_expand_factory,
             bool create_components = true);
 
-  virtual ~NetEqImpl();
+  ~NetEqImpl() override;
 
   // Inserts a new packet into NetEq. The |receive_timestamp| is an indication
   // of the time when the packet was received, and should be measured with
@@ -133,11 +133,11 @@
 
   int LeastRequiredDelayMs() const override;
 
-  int SetTargetDelay() override { return kNotImplemented; }
+  int SetTargetDelay() override;
 
-  int TargetDelay() override { return kNotImplemented; }
+  int TargetDelay() override;
 
-  int CurrentDelay() override { return kNotImplemented; }
+  int CurrentDelay() override;
 
   // Sets the playout mode to |mode|.
   // Deprecated.
@@ -174,9 +174,9 @@
 
   bool GetPlayoutTimestamp(uint32_t* timestamp) override;
 
-  int SetTargetNumberOfChannels() override { return kNotImplemented; }
+  int SetTargetNumberOfChannels() override;
 
-  int SetTargetSampleRate() override { return kNotImplemented; }
+  int SetTargetSampleRate() override;
 
   // Returns the error code for the last occurred error. If no error has
   // occurred, 0 is returned.