Add extended header containing frame ID to the generic packetizer.

Also changes default value of frame ID in RTPVideoHeader to
kNoPictureId. Special care should be take so that picture ID will not
be set in RTPVideoHeader unless the client on the end supports
deserializing extended generic header.

Bug: webrtc:9582
Change-Id: Ib096373ed187f31e51d481193a2bda56de68f167
Reviewed-on: https://webrtc-review.googlesource.com/92084
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24250}

modules/rtp_rtcp/source/rtp_format.cc

@@ -41,7 +41,9 @@ RtpPacketizer* RtpPacketizer::Create(VideoCodecType type,
                                   last_packet_reduction_len);
     }
     case kVideoCodecGeneric:
-      return new RtpPacketizerGeneric(frame_type, max_payload_len,
+      RTC_CHECK(rtp_video_header);
+      return new RtpPacketizerGeneric(*rtp_video_header, frame_type,
+                                      max_payload_len,
                                       last_packet_reduction_len);
     default:
       RTC_NOTREACHED();