Add Generic frame descritpor header extension

to list of extensions supported by RtpPacket.

Bug: webrtc:9361
Change-Id: Iabee824381be3776e17e95f32507058607fc0bc8
Reviewed-on: https://webrtc-review.googlesource.com/85346
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Alex Loiko <aleloi@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23788}

modules/rtp_rtcp/include/rtp_rtcp_defines.h

@@ -110,6 +110,7 @@ enum RTPExtensionType {
   kRtpExtensionRtpStreamId,
   kRtpExtensionRepairedRtpStreamId,
   kRtpExtensionMid,
+  kRtpExtensionGenericFrameDescriptor,
   kRtpExtensionNumberOfExtensions  // Must be the last entity in the enum.
 };