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/ulpfec_generator.h

@@ -24,6 +24,7 @@ class FlexfecSender;
 class RedPacket {
  public:
   explicit RedPacket(size_t length);
+  ~RedPacket();
 
   void CreateHeader(const uint8_t* rtp_header,
                     size_t header_length,