nokia-n900: fix xfce4 background (!748)

[ci:skip-build]: already built successfully in CI

device/device-nokia-n900/APKBUILD

@@ -1,7 +1,7 @@
 # Reference: <https://postmarketos.org/devicepkg>
 pkgname=device-nokia-n900
 pkgver=5
-pkgrel=0
+pkgrel=1
 pkgdesc="Nokia N900"
 url="https://postmarketos.org"
 arch="armv7"
@@ -13,6 +13,7 @@ subpackages="
 	$pkgname-weston
 	$pkgname-x11
 	$pkgname-i3wm
+	$pkgname-xfce4
 	$pkgname-nonfree-firmware:nonfree_firmware
 "
 source="
@@ -132,6 +133,12 @@ i3wm() {
 		"$subpkgdir"/etc/sudoers.d/10-noroot-suspend
 }
 
+xfce4() {
+	install_if="$pkgname postmarketos-ui-xfce4"
+	install="$subpkgname.post-install"
+	mkdir "$subpkgdir"
+}
+
 nonfree_firmware() {
 	pkgdesc="Wifi firmware"
 	depends="linux-firmware-ti-connectivity"

device/device-nokia-n900/device-nokia-n900-xfce4.post-install

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+sed -i 's/monitor0/monitorLVDS-1/' /etc/skel/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-desktop.xml
+