base: Add ret to common svc req elements

We're logging SUCCESS even when the KDC sends error replies.  That's
because we're returning success to process_request() even when we send
errors to clients.  The error we want to send to the client, and that we
succeed or fail to send it, are different statuses.

To fix this we'll add a `ret` field to the common service request state
structure, HEIM_SVC_REQUEST_DESC_COMMON_ELEMENTS /
heim_svc_req_desc_common_s.

lib/base/log.c

@@ -820,7 +820,7 @@ heim_audit_trail(heim_svc_req_desc r, heim_error_code ret, const char *retname)
 #define CASE(x)	case x : retval = #x; break
     if (retname) {
         retval = retname;
-    } else switch (ret) {
+    } else switch (ret ? ret : r->ret) {
     CASE(ENOMEM);
     CASE(ENOENT);
     CASE(EACCES);