Allow pass max-silent-time and build-poll-interval to daemon untrusted

These settings seem harmless, they control the same polling
functionality that timeout does, but with different behavior. Should
be safe for untrusted users to pass in.

src/libstore/daemon.cc

@@ -239,6 +239,8 @@ struct ClientSettings
                 else if (trusted
                     || name == settings.buildTimeout.name
                     || name == settings.buildRepeat.name
+                    || name == settings.maxSilentTime.name
+                    || name == settings.pollInterval.name
                     || name == "connect-timeout"
                     || (name == "builders" && value == ""))
                     settings.set(name, value);