comgt: ncm: allow specification of interface name

Add ifname property to UCI, which can be used to override the
autodetected interface name in case the detection fails due to having
none or more than one interface exposed by the modem, which is not
explicitly linked to TTY port. This is needed on certain variants of ZTE
MF286R built-in modem, which exposes both RNDIS and CDC-ECM interfaces
on the modem, on which the automatic detection may select the wrong
network interface.

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>

package/network/utils/comgt/files/ncm.sh

@@ -10,6 +10,7 @@ proto_ncm_init_config() {
 	no_device=1
 	available=1
 	proto_config_add_string "device:device"
+	proto_config_add_string ifname
 	proto_config_add_string apn
 	proto_config_add_string auth
 	proto_config_add_string username
@@ -25,10 +26,10 @@ proto_ncm_init_config() {
 proto_ncm_setup() {
 	local interface="$1"
 
-	local manufacturer initialize setmode connect finalize ifname devname devpath
+	local manufacturer initialize setmode connect finalize devname devpath
 
-	local device apn auth username password pincode delay mode pdptype profile $PROTO_DEFAULT_OPTIONS
-	json_get_vars device apn auth username password pincode delay mode pdptype profile $PROTO_DEFAULT_OPTIONS
+	local device ifname  apn auth username password pincode delay mode pdptype profile $PROTO_DEFAULT_OPTIONS
+	json_get_vars device ifname apn auth username password pincode delay mode pdptype profile $PROTO_DEFAULT_OPTIONS
 
 	[ "$metric" = "" ] && metric="0"
 
@@ -53,17 +54,20 @@ proto_ncm_setup() {
 		return 1
 	}
 
-	devname="$(basename "$device")"
-	case "$devname" in
-	'tty'*)
-		devpath="$(readlink -f /sys/class/tty/$devname/device)"
-		ifname="$( ls "$devpath"/../../*/net )"
-		;;
-	*)
-		devpath="$(readlink -f /sys/class/usbmisc/$devname/device/)"
-		ifname="$( ls "$devpath"/net )"
-		;;
-	esac
+	[ -z "$ifname" ] && {
+		devname="$(basename "$device")"
+		case "$devname" in
+		'tty'*)
+			devpath="$(readlink -f /sys/class/tty/$devname/device)"
+			ifname="$( ls "$devpath"/../../*/net )"
+			;;
+		*)
+			devpath="$(readlink -f /sys/class/usbmisc/$devname/device/)"
+			ifname="$( ls "$devpath"/net )"
+			;;
+		esac
+	}
+
 	[ -n "$ifname" ] || {
 		echo "The interface could not be found."
 		proto_notify_error "$interface" NO_IFACE