(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}

pc/sctp_utils.h

@@ -8,12 +8,12 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef PC_SCTPUTILS_H_
-#define PC_SCTPUTILS_H_
+#ifndef PC_SCTP_UTILS_H_
+#define PC_SCTP_UTILS_H_
 
 #include <string>
 
-#include "api/datachannelinterface.h"
+#include "api/data_channel_interface.h"
 
 namespace rtc {
 class CopyOnWriteBuffer;
@@ -38,4 +38,4 @@ bool WriteDataChannelOpenMessage(const std::string& label,
 void WriteDataChannelOpenAckMessage(rtc::CopyOnWriteBuffer* payload);
 }  // namespace webrtc
 
-#endif  // PC_SCTPUTILS_H_
+#endif  // PC_SCTP_UTILS_H_