lockd: Rename struct nlm_lock to lockd_lock

lockd: Rename struct nlm_lock to lockd_lock

A subsequent patch will convert fs/lockd/svcproc.c to use
machine-generated XDR encoding and decoding functions in a
manner similar to fs/lockd/svc4proc.c. Machine-generated
types derived from the NLM specification will conflict with
the internal types of the same name.

Rename the internal struct nlm_lock type to lockd_lock to
avoid such naming conflicts.

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