Make OverheadObserver::OnOverheadChanged count RTP headers only

webrtc/modules/rtp_rtcp/source/rtcp_sender.h

Index: webrtc/modules/rtp_rtcp/source/rtcp_sender.h
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_sender.h b/webrtc/modules/rtp_rtcp/source/rtcp_sender.h
index 3dbbb3e3405e066970b0ef8eea8aea1bf80cd641..96a49a72e0718e232215bb1e70703631c6d9d5d2 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_sender.h
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_sender.h
@@ -133,7 +133,7 @@ class RTCPSender {
 
   void SetTMMBRStatus(bool enable);
 
-  void SetMaxPayloadLength(size_t max_payload_length);
+  void SetMaxRtpPacketSize(size_t max_packet_size);
 
   void SetTmmbn(std::vector<rtcp::TmmbItem> bounding_set);
 
@@ -240,7 +240,7 @@ class RTCPSender {
       GUARDED_BY(critical_section_rtcp_sender_);
   uint32_t tmmbr_send_bps_ GUARDED_BY(critical_section_rtcp_sender_);
   uint32_t packet_oh_send_ GUARDED_BY(critical_section_rtcp_sender_);
-  size_t max_payload_length_;
+  size_t max_packet_size_;
 
   // APP
   uint8_t app_sub_type_ GUARDED_BY(critical_section_rtcp_sender_);