[rtp_rtcp] Lint build/header_guard errors fixed

BUG=webrtc:5277
R=mflodman

Review URL: https://codereview.webrtc.org/1506043003

Cr-Commit-Position: refs/heads/master@{#10949}

webrtc/modules/rtp_rtcp/test/testAPI/test_api.h

@@ -7,6 +7,8 @@
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
+#ifndef WEBRTC_MODULES_RTP_RTCP_TEST_TESTAPI_TEST_API_H_
+#define WEBRTC_MODULES_RTP_RTCP_TEST_TESTAPI_TEST_API_H_
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/base/scoped_ptr.h"
@@ -68,3 +70,4 @@ class TestRtpReceiver : public NullRtpData {
 };
 
 }  // namespace webrtc
+#endif  // WEBRTC_MODULES_RTP_RTCP_TEST_TESTAPI_TEST_API_H_