datasets: comment to specify usage of field

src/detect-dataset.h

@@ -33,7 +33,7 @@ typedef struct DetectDatasetData_ {
     DatasetFormats format;
     DataJsonType json;
     char json_key[SIG_JSON_CONTENT_KEY_LEN];
-    void *id;
+    void *id; /* pointer to the triggering signature */
 } DetectDatasetData;
 
 int DetectDatasetBufferMatch(DetectEngineThreadCtx *det_ctx,

src/detect.h

@@ -1234,7 +1234,7 @@ typedef struct PostRuleMatchWorkQueue {
 
 /** structure to store the json content with info on sig that triggered it */
 typedef struct SigJsonContent {
-    void *id;
+    void *id; /**< pointer to the sig that triggered this json content */
     char json_content[SIG_JSON_CONTENT_ITEM_LEN];
 } SigJsonContent;