NSM: Encode the new "priv" cookie for NSMPROC_MON requests

Pass the new "priv" cookie to NSMPROC_MON's XDR encoder, instead of
creating the "priv" argument in the encoder at call time.

This patch should not cause a behavioral change: the contents of the
cookie remain the same for the time being.

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