Fix clang style errors in rtp_rtcp and dependant targets

Mark functions with override instead of virtual.
Add explicit non-trivial constructors/assign operators/destructors.
Define them in .cc files instead of inlining
use auto* instead of auto when deduced type is raw pointer

Bug: webrtc:163
Change-Id: I4d8a05d6a64fcc2ca16d02c5fcf9488fda832a6d
Reviewed-on: https://webrtc-review.googlesource.com/48781
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21927}

logging/rtc_event_log/rtc_event_log.h

@@ -57,9 +57,7 @@ class RtcEventLog {
 class RtcEventLogNullImpl : public RtcEventLog {
  public:
   bool StartLogging(std::unique_ptr<RtcEventLogOutput> output,
-                    int64_t output_period_ms) override {
-    return false;
-  }
+                    int64_t output_period_ms) override;
   void StopLogging() override {}
   void Log(std::unique_ptr<RtcEvent> event) override {}
 };