Constify req.body pointer when interating over it.

bin/varnishd/cache/cache.h

@@ -682,7 +682,8 @@ void VBO_waitstate(struct busyobj *bo, enum busyobj_state_e want);
 /* cache_req_body.c */
 int VRB_Ignore(struct req *req);
 ssize_t VRB_Cache(struct req *req, ssize_t maxsize);
-typedef int (req_body_iter_f)(struct req *, void *priv, void *ptr, size_t);
+typedef int (req_body_iter_f)(struct req *, void *priv,
+    const void *ptr, size_t);
 ssize_t VRB_Iterate(struct req *req, req_body_iter_f *func, void *priv);
 void VRB_Free(struct req *req);
 

bin/varnishd/cache/cache_req_body.c

@@ -147,7 +147,7 @@ VRB_Iterate(struct req *req, req_body_iter_f *func, void *priv)
  */
 
 static int __match_proto__(req_body_iter_f)
-httpq_req_body_discard(struct req *req, void *priv, void *ptr, size_t len)
+httpq_req_body_discard(struct req *req, void *priv, const void *ptr, size_t len)
 {
 
 	CHECK_OBJ_NOTNULL(req, REQ_MAGIC);

bin/varnishd/http1/cache_http1_fetch.c

@@ -49,7 +49,7 @@
  */
 
 static int __match_proto__(req_body_iter_f)
-vbf_iter_req_body(struct req *req, void *priv, void *ptr, size_t l)
+vbf_iter_req_body(struct req *req, void *priv, const void *ptr, size_t l)
 {
 	struct busyobj *bo;