SUNRPC: Use correct XDR encoding procedure for rpcbind SET/UNSET

The rpcbind versions 3 and 4 SET and UNSET procedures use the same
arguments as the GETADDR procedure.

While definitely a bug, this hasn't been a problem so far since the
kernel hasn't used version 3 or 4 SET and UNSET.  But this will change
in just a moment.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>