Corrected check for websocket connection close

mongoose.c

@@ -4103,9 +4103,9 @@ static void read_websocket(struct mg_connection *conn) {
 
       // Exit the loop if callback signalled to exit,
       // or "connection close" opcode received.
-      if ((conn->ctx->callbacks.websocket_data != NULL &&
-          !conn->ctx->callbacks.websocket_data(conn, bits, data, data_len)) ||
-          (bits & 0xf) == 8) {  // Opcode == 8, connection close
+      if ((bits & WEBSOCKET_OPCODE_CONNECTION_CLOSE) ||
+          (conn->ctx->callbacks.websocket_data != NULL &&
+           !conn->ctx->callbacks.websocket_data(conn, bits, data, data_len))) {
         stop = 1;
       }