flow: reduce structure size by removing gap

src/flow.h

@@ -374,9 +374,6 @@ typedef struct Flow_
 
     uint32_t flags;         /**< generic flags */
 
-    /* Parent flow id for protocol like ftp */
-    int64_t parent_id;
-
     uint16_t file_flags;    /**< file tracking/extraction flags */
     /* coccinelle: Flow:file_flags:FLOWFILE_ */
 
@@ -384,6 +381,9 @@ typedef struct Flow_
      *  for use with STARTTLS and HTTP CONNECT detection */
     uint16_t protodetect_dp; /**< 0 if not used */
 
+    /* Parent flow id for protocol like ftp */
+    int64_t parent_id;
+
 #ifdef FLOWLOCK_RWLOCK
     SCRWLock r;
 #elif defined FLOWLOCK_MUTEX