Provide workaround for kmod/initramfs-tools issue with NFS/netboot

Provide workaround for kmod/initramfs-tools issue with NFS/netboot

As of kmod v30+20220905-1 (as present in current Debian/bookworm), the
output of the "modprobe --all --set-version="..." --ignore-install
--quiet --show-depends nfs" command line, as used by initramfs-tools to
identify dependencies of the the nfs module, changed. See
https://bugs.debian.org/1022172 for further details.

Until the situation between kmod, /lib/modprobe.d/50-nfs.conf and
initramfs-tools has been resolved, let's provide a workaround, so our
initramfs includes the required modules for netboot usage with NFS.

Thanks: András Korn
Closes: https://github.com/grml/grml/issues/192