(4) Rename files to snake_case: update BUILD.gn, include paths, header guards, and DEPS entries

Mechanically generated by running this command:

tools_webrtc/do-renames.sh update all-renames.txt && git cl format

Then manually updating:

tools_webrtc/sanitizers/tsan_suppressions_webrtc.cc

Bug: webrtc:10159
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I54824cd91dada8fc3ee3d098f971bc319d477833
Reviewed-on: https://webrtc-review.googlesource.com/c/115653
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26226}
diff --git a/api/ortc/rtp_transport_interface.h b/api/ortc/rtp_transport_interface.h
index 4b9d161..ec71216 100644
--- a/api/ortc/rtp_transport_interface.h
+++ b/api/ortc/rtp_transport_interface.h
@@ -8,16 +8,16 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef API_ORTC_RTPTRANSPORTINTERFACE_H_
-#define API_ORTC_RTPTRANSPORTINTERFACE_H_
+#ifndef API_ORTC_RTP_TRANSPORT_INTERFACE_H_
+#define API_ORTC_RTP_TRANSPORT_INTERFACE_H_
 
 #include <string>
 
 #include "absl/types/optional.h"
-#include "api/ortc/packettransportinterface.h"
-#include "api/rtcerror.h"
+#include "api/ortc/packet_transport_interface.h"
+#include "api/rtc_error.h"
 #include "api/rtp_headers.h"
-#include "api/rtpparameters.h"
+#include "api/rtp_parameters.h"
 
 namespace webrtc {
 
@@ -91,4 +91,4 @@
 
 }  // namespace webrtc
 
-#endif  // API_ORTC_RTPTRANSPORTINTERFACE_H_
+#endif  // API_ORTC_RTP_TRANSPORT_INTERFACE_H_