修复webrtc推流互斥锁重入死锁bug (#2713)

simulcast推流时，在onRecvRtp函数中可能触发对totalReaderCount的调用，从而导致死锁。

webrtc/WebRtcPusher.cpp

@@ -61,7 +61,7 @@ bool WebRtcPusher::close(MediaSource &sender) {
 int WebRtcPusher::totalReaderCount(MediaSource &sender) {
     auto total_count = _push_src ? _push_src->totalReaderCount() : 0;
     if (_simulcast) {
-        std::lock_guard<std::mutex> lock(_mtx);
+        std::lock_guard<std::recursive_mutex> lock(_mtx);
         for (auto &src : _push_src_sim) {
             total_count += src.second->totalReaderCount();
         }
@@ -99,7 +99,7 @@ void WebRtcPusher::onRecvRtp(MediaTrack &track, const string &rid, RtpPacket::Pt
         }
     } else {
         //视频
-        std::lock_guard<std::mutex> lock(_mtx);
+        std::lock_guard<std::recursive_mutex> lock(_mtx);
         auto &src = _push_src_sim[rid];
         if (!src) {
             const auto& stream = _push_src->getMediaTuple().stream;