README: info about dhcpd's 'ignore-client-uids'
Network drivers moved to a separate initramfs file

No need to include those in the main 'init.cpi', they will be rarely
needed.
udhcpc.script fixes
Clean up after initramfs

Most of _init.cpi files must stay as they are not separately packaged in
any of the squashfs images, but _net.cpi is optional, so the files must
be provided in the squashfs modules, the initramfs copies may be safely
removed.

Also, the init scripts from _init.cpi are removed, as they are not
needed in the final system.