Add a systemd generator for root=nbd:.. so that systemd has a correct
sysroot.mount unit.
Use export names instead of port numbers, because port number based
exports are deprecated and were removed.
With this change, we can now use LUKS and LVM over NBD. There are
some decisions to be made regarding where we should get the fstype
and fsoptions from (DHCP root vs rootfstype= etc), but the basic
functionality is there.
Harald Hoyer