tree-wide: warn when sd_notify fails with READY=1 or FDSTOREREMOVE=1

Most sd_notify() calls are like log_info() — the result is only informative
and if they fail, it's best ignore this. But if a call with READY=1 fails,
the unit may enter a failed state, so we should warn about this. Similarly
for FSTOREREMOVE=1: the manager may be left with a stale fd, at least wasting
resources.

src/rfkill/rfkill.c

@@ -317,7 +317,10 @@ static int run(int argc, char *argv[]) {
                         if (!ready) {
                                 /* Notify manager that we are now finished with processing whatever was
                                  * queued */
-                                (void) sd_notify(false, "READY=1");
+                                r = sd_notify(false, "READY=1");
+                                if (r < 0)
+                                        log_warning_errno(r, "Failed to send readiness notification, ignoring: %m");
+
                                 ready = true;
                         }