cmd/cli: use OS resolver as default upstream for SRV lan hostname

Since application may need SRV record for public domains, which could be
blocked by OS resolver, but not with remote upstreams.

This was reported by a Minecraft user, who seeing thing is broken after
upgrading to v1.4.0 release.

cmd/cli/prog.go

@@ -43,7 +43,7 @@ const (
 	ctrldControlUnixSockMobile = "cd.sock"
 	upstreamPrefix             = "upstream."
 	upstreamOS                 = upstreamPrefix + "os"
-	upstreamPrivate            = upstreamPrefix + "private"
+	upstreamOSLocal            = upstreamOS + ".local"
 	dnsWatchdogDefaultInterval = 20 * time.Second
 	ctrldServiceName           = "ctrld"
 )