add locks around Socket::send and Socket::recv to see if it helps with thread sanitizer error in Linux CI

ixwebsocket/IXSocket.cpp

@@ -160,6 +160,8 @@ namespace ix
 
     ssize_t Socket::send(char* buffer, size_t length)
     {
+        std::lock_guard<std::mutex> lock(_socketMutex);
+
         int flags = 0;
 #ifdef MSG_NOSIGNAL
         flags = MSG_NOSIGNAL;
@@ -175,6 +177,8 @@ namespace ix
 
     ssize_t Socket::recv(void* buffer, size_t length)
     {
+        std::lock_guard<std::mutex> lock(_socketMutex);
+
         int flags = 0;
 #ifdef MSG_NOSIGNAL
         flags = MSG_NOSIGNAL;