Introduce utility flow macros to help referencing/dereferencing flows.

src/flow-util.h

@@ -127,6 +127,16 @@
 #define FLOW_CHECK_MEMCAP(size) \
     ((((uint64_t)SC_ATOMIC_GET(flow_memuse) + (uint64_t)(size)) <= flow_config.memcap))
 
+#define FlowReference(dst_f_ptr, f) do {        \
+        FlowIncrUsecnt((f));                    \
+        *(dst_f_ptr) = f;                       \
+    } while (0)
+
+#define FlowDeReference(src_f_ptr) do {           \
+        FlowDecrUsecnt(*(src_f_ptr));   \
+        *(src_f_ptr) = NULL;                      \
+    } while (0)
+
 Flow *FlowAlloc(void);
 Flow *FlowAllocDirect(void);
 void FlowFree(Flow *);