Add a safety belt assignment to the nfsd for when "-p" isn't specified.

The kernel code assumes that nfsdargs.addr == NULL and nfsdargs.addrlen == 0
when there is no "-p" argument used for starting the nfsd.
This small patch ensures this is the case. In practice, I believe this always
happened, since "nfsdargs" was the last element on the stack for "main()",
but this little patch ensures it will be the case.
Spotted by inspection while adding a new optional field for "-p".