[rtp_rtcp] fixed namespaces lint warnings

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

Index: webrtc/modules/rtp_rtcp/test/testAPI/test_api.cc
diff --git a/webrtc/modules/rtp_rtcp/test/testAPI/test_api.cc b/webrtc/modules/rtp_rtcp/test/testAPI/test_api.cc
index d245d103b835865aa1db31f46f8a80fbd6004567..1d4d6d04a5e3a281c8946fd8adbfd56bd44c1f7f 100644
--- a/webrtc/modules/rtp_rtcp/test/testAPI/test_api.cc
+++ b/webrtc/modules/rtp_rtcp/test/testAPI/test_api.cc
@@ -15,9 +15,8 @@
 
 #include "webrtc/test/null_transport.h"
 
-using namespace webrtc;
-
 namespace webrtc {
+
 void LoopBackTransport::SetSendModule(RtpRtcp* rtp_rtcp_module,
                                       RTPPayloadRegistry* payload_registry,
                                       RtpReceiver* receiver,
@@ -77,7 +76,6 @@ int32_t TestRtpReceiver::OnReceivedPayloadData(
   payload_size_ = payload_size;
   return 0;
 }
-}  // namespace webrtc
 
 class RtpRtcpAPITest : public ::testing::Test {
  protected:
@@ -188,3 +186,5 @@ TEST_F(RtpRtcpAPITest, RtxReceiver) {
   rtx_header.payloadType = 0;
   EXPECT_TRUE(rtp_payload_registry_->IsRtx(rtx_header));
 }
+
+}  // namespace webrtc