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}

modules/rtp_rtcp/source/rtp_header_parser.cc

@@ -18,7 +18,7 @@ namespace webrtc {
 class RtpHeaderParserImpl : public RtpHeaderParser {
  public:
   RtpHeaderParserImpl();
-  virtual ~RtpHeaderParserImpl() {}
+  ~RtpHeaderParserImpl() override = default;
 
   bool Parse(const uint8_t* packet,
              size_t length,