lockd: Rename struct nlm_reboot to lockd_reboot

lockd: Rename struct nlm_reboot to lockd_reboot

As part of the effort to enable lockd's server-side XDR functions to
be generated from the NLM protocol specification (using xdrgen), the
internal type names must be changed to avoid conflicts with the
machine-generated type names.

Rename struct nlm_reboot to struct lockd_reboot for consistency with
the other renamed internal types.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>