lockd: Do not monitor when looking up the LOCK_MSG callback host

lockd: Do not monitor when looking up the LOCK_MSG callback host

A LOCK_MSG handler that fails to obtain a host returns
rpc_system_err, which causes the dispatcher to send an RPC-level
error rather than an NLM LOCK_RES denial. Before the xdrgen
conversion, the outer host lookup was unmonitored, so an NSM
upcall failure was reported back to the client through LOCK_RES
with status nlm_lck_denied_nolocks generated by the inner helper.

The xdrgen conversion replaced the unmonitored lookup with
nlm4svc_lookup_host(..., true). When nsm_monitor() fails, the
outer lookup now returns NULL, so the procedure short-circuits to
rpc_system_err and __nlm4svc_proc_lock_msg() never runs. The
client therefore receives no LOCK_RES, regressing the legacy
behavior.

The inner helper still performs a monitored lookup while building
the LOCK_RES, so the outer call only needs an unmonitored host
reference for the callback path. Pass false here to restore the
previous semantics.

Fixes: b2be4e28c23a ("lockd: Use xdrgen XDR functions for the NLMv4 LOCK_MSG procedure")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>