add a rate-limit.

src/or/consdiffmgr.c

@@ -1311,8 +1311,10 @@ store_multiple(consensus_cache_entry_handle_t **handles_out,
                             body_out,
                             bodylen_out);
       if (ent == NULL) {
-        log_warn(LD_FS, "Unable to store object %s compressed with %s.",
-                 description, methodname);
+        static ratelim_t cant_store_ratelim = RATELIM_INIT(5*70);
+        log_fn_ratelim(&cant_store_ratelim, LOG_WARN, LD_FS,
+                       "Unable to store object %s compressed with %s.",
+                       description, methodname);
         continue;
       }