[rtp_rtcp] fixed namespaces lint warnings

webrtc/modules/rtp_rtcp/source/rtcp_receiver_help.cc

Index: webrtc/modules/rtp_rtcp/source/rtcp_receiver_help.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_receiver_help.cc b/webrtc/modules/rtp_rtcp/source/rtcp_receiver_help.cc
index 718990d10b5881cd116f3ebc7b8fd1257e16be2c..a5c0e2828282fad6bef0d695980542dec5c00c43 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_receiver_help.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_receiver_help.cc
@@ -17,7 +17,7 @@
 #include "webrtc/modules/rtp_rtcp/source/rtp_utility.h"
 
 namespace webrtc {
-using namespace RTCPHelp;
+namespace RTCPHelp {
 
 RTCPPacketInformation::RTCPPacketInformation()
     : rtcpPacketTypeFlags(0),
@@ -190,4 +190,5 @@ void RTCPReceiveInformation::VerifyAndAllocateBoundingSet(
     const uint32_t minimumSize) {
   TmmbnBoundingSet.VerifyAndAllocateSet(minimumSize);
 }
+}  // namespace RTCPHelp
 }  // namespace webrtc