Switch to using Ubuntu installer kernel updates

src/ubuntu.ipxe

@@ -26,12 +26,12 @@ set ubuntu_mirror old-releases.ubuntu.com
 echo Setting mirror to ${ubuntu_mirror}
 clear ubuntu_version
 echo -n Please set enter code name of release: ${} && read ubuntu_version
-set dir ${ubuntu_base_dir}/dists/${ubuntu_version}/main/installer-${arch_a}/current/images/netboot/
+set dir ${ubuntu_base_dir}/dists/${ubuntu_version}-updates/main/installer-${arch_a}/current/images/netboot/
 goto deb_boot_type
 
 :mirrorcfg
 set mirrorcfg mirror/suite=${ubuntu_version}
-set dir ${ubuntu_base_dir}/dists/${ubuntu_version}/main/installer-${arch_a}/current/images/netboot/
+set dir ${ubuntu_base_dir}/dists/${ubuntu_version}-updates/main/installer-${arch_a}/current/images/netboot/
 
 :deb_boot_type
 menu ${os} [${ubuntu_version}] Installer