NLM: Change nlm_host_rebooted() to take a single nlm_reboot argument

Pass the nlm_reboot data structure directly from the NLMPROC_SM_NOTIFY
XDR decoders to nlm_host_rebooted().  This eliminates some packing and
unpacking of the NLMPROC_SM_NOTIFY results, and prepares for passing
these results, including the "priv" cookie, directly to a lookup
routine in fs/lockd/mon.c.

This patch changes code organization but should not cause any
behavioral change.

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