transaction inspection: fix limit enforcement

Make sure we're never wrapping around the size value.

src/detect-engine-hcbd.c

@@ -64,7 +64,7 @@
 
 static inline int HCBDCreateSpace(DetectEngineThreadCtx *det_ctx, uint64_t size)
 {
-    if (size >= USHRT_MAX)
+    if (size >= (USHRT_MAX - BUFFER_STEP))
         return -1;
 
     void *ptmp;

src/detect-engine-hhd.c

@@ -62,7 +62,7 @@
 
 static inline int HHDCreateSpace(DetectEngineThreadCtx *det_ctx, uint64_t size)
 {
-    if (size >= USHRT_MAX)
+    if (size >= (USHRT_MAX - BUFFER_STEP))
         return -1;
 
     void *ptmp;

src/detect-engine-hsbd.c

@@ -66,7 +66,7 @@
 
 static inline int HSBDCreateSpace(DetectEngineThreadCtx *det_ctx, uint64_t size)
 {
-    if (size >= USHRT_MAX)
+    if (size >= (USHRT_MAX - BUFFER_STEP))
         return -1;
 
     void *ptmp;