Fixing neteq_rtpplay

A regression happened in https://codereview.webrtc.org/2006723002,
causing neteq_rtpplay not to work. The problem was that when the main
code was moved inside of the webrtc::test namespace, it was no longer
visible to the linker. Meanwhile, the dependency on test_support_main
rather than test_support caused the executable to be a gtest.

In this fix, the gyp dependencies are corrected, and a main method is
added outside of the namespaces.

NOTRY=True

Review-Url: https://codereview.webrtc.org/2018473002
Cr-Commit-Position: refs/heads/master@{#12918}

webrtc/modules/audio_coding/neteq/tools/neteq_rtpplay.cc

@@ -368,9 +368,7 @@ size_t ReplacePayload(InputAudioFile* replacement_audio_file,
   return payload_len;
 }
 
-}  // namespace
-
-int main(int argc, char* argv[]) {
+int RunTest(int argc, char* argv[]) {
   static const int kOutputBlockSizeMs = 10;
 
   std::string program_name = argv[0];
@@ -632,5 +630,10 @@ int main(int argc, char* argv[]) {
   return 0;
 }
 
+}  // namespace
 }  // namespace test
 }  // namespace webrtc
+
+int main(int argc, char* argv[]) {
+  webrtc::test::RunTest(argc, argv);
+}