appliance: enable bash's Process Substitution feature

bash can read input from a spawned process, and even provide input to
such process. This feature relies on /dev/fd/ being present. In the
past udev silently created this symlink, so this bash feature worked
more or less by accident. With recent systemd versions, such as 246
which is included in Leap 15.3, the symlink is not created anymore. As
a result scripts, such as /sbin/dhclient-script, fail to work
properly.

This symlink should have been created in version 1 of this variant of /init.

https://bugzilla.opensuse.org/show_bug.cgi?id=1190501

Signed-off-by: Olaf Hering <olaf@aepfle.de>

appliance/init

@@ -72,6 +72,7 @@ fi
 
 # devtmpfs is required since udev 176
 mount -t devtmpfs /dev /dev
+ln -s /proc/self/fd /dev/fd
 mkdir -p /dev/pts
 mount -t devpts /dev/pts /dev/pts
 mkdir -p /dev/shm