pxe: fix path of linux and initrd

pxe/install-pxe.sh

@@ -26,6 +26,7 @@ install_nfs() {
         cat > /etc/exports <<END
 ${nfs_path} ${nfs_allowed_lan}(rw,sync,no_subtree_check,no_root_squash)
 END
+        mkdir -p "${nfs_path}"
 }
 
 install_tftp() {
@@ -51,8 +52,8 @@ install_netboot() {
 default wb
 
 label wb
-        KERNEL vmlinuz
-        INITRD initd.img
+        KERNEL debian-installer/amd64/linux
+        INITRD debian-installer/amd64/initd.gz
         APPEND ip=dhcp netboot=nfs nfsroot=${server_ip}:${nfs_path}/ boot=live text forcepae
 END
         fi