Use non updates dir for Ubuntu 20.04

focal-updates isn't available yet so use regular
url. also location has changed to legacy-images
from images

roles/netbootxyz/templates/menu/ubuntu.ipxe.j2

@@ -31,7 +31,7 @@ goto deb_boot_type
 :mirrorcfg
 set mirrorcfg mirror/suite=${ubuntu_version}
 set dir ${ubuntu_base_dir}/dists/${ubuntu_version}-updates/main/installer-${arch_a}/current/images/netboot/
-iseq ${ubuntu_version} focal && set dir ${ubuntu_base_dir}/dists/${ubuntu_version}/main/installer-${arch_a}/current/images/netboot/ ||
+iseq ${ubuntu_version} focal && set dir ${ubuntu_base_dir}/dists/${ubuntu_version}/main/installer-${arch_a}/current/legacy-images/netboot/ ||
 
 :deb_boot_type
 menu ${os} [${ubuntu_version}] Installer