qos-scripts: fix interface resolving

Also ensure that the error message is actually printed to stderr and that
the rule generation is aborted if an interface cannot be resolved.

Ref: https://github.com/openwrt/luci/issues/3975
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 559b3384666bbc6e4e9e6d86cf54bd88d30b341f)

package/network/config/qos-scripts/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=qos-scripts
 PKG_VERSION:=1.3.1
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 PKG_LICENSE:=GPL-2.0
 
 PKG_MAINTAINER:=Felix Fietkau <nbd@nbd.name>

package/network/config/qos-scripts/files/usr/lib/qos/generate.sh

@@ -22,15 +22,20 @@ add_insmod() {
 [ -e /etc/config/network ] && {
 	# only try to parse network config on librecmc
 
-	find_ifname() {(
-		reset_cb
-		include /lib/network
-		scan_interfaces
-		config_get "$1" ifname
-	)}
+	. /lib/functions/network.sh
+
+	find_ifname() {
+		local ifname
+		if network_get_device ifname "$1"; then
+			echo "$ifname"
+		else
+			echo "Device for interface $1 not found." >&2
+			exit 1
+		fi
+	}
 } || {
 	find_ifname() {
-		echo "Interface not found."
+		echo "Interface not found." >&2
 		exit 1
 	}
 }
@@ -218,6 +223,7 @@ qos_parse_config() {
 				config_get device "$1" device
 				[ -z "$device" ] && {
 					device="$(find_ifname $1)"
+					[ -z "$device" ] && exit 1
 					config_set "$1" device "$device"
 				}
 			}