Comment # 18 on bug 1200710 from Neil Brown

Sorry about this.  I hadn't imagined the modprobe.d file being installed
somewhere that sysctl didn't exist.
One option might be to blacklist the file from the initramfs.
However it is probably easier to make the scriptlet safe.

 install sunrpc /sbin/modprobe .... && { /sbin/sysctl .... ; exit 0 ; }

seems to work.  I'll submit an update.