lockd: Use xdrgen XDR functions for the NLMv3 GRANTED procedure

lockd: Use xdrgen XDR functions for the NLMv3 GRANTED procedure

The NLM GRANTED procedure allows servers to notify clients when
a previously blocked lock request has been granted, completing
the asynchronous lock request flow. This patch converts the NLMv3
GRANTED procedure to use xdrgen-generated XDR functions.

The conversion replaces the legacy decoder with the xdrgen
functions nlm_svc_decode_nlm_testargs and nlm_svc_encode_nlm_res
generated from the NLM version 3 protocol specification. The
procedure handler accesses xdrgen types through a wrapper structure
that bridges between generated code and the legacy lockd_lock
representation still used by the core lockd logic.

A new helper function nlm_lock_to_lockd_lock() converts an xdrgen
nlm_lock into the legacy lockd_lock format. The helper complements
the existing nlm3svc_lookup_host() and nlm3svc_lookup_file()
functions used throughout this series.

Setting pc_argzero to zero is safe because the generated decoder
fills the argp->xdrgen subfields before the procedure runs, so the
zeroing memset performed by the dispatch layer is not needed. The
helper populates each field of the wrapper's lock member that any
downstream consumer reads: fh, oh, svid, and the file_lock byte
range. Because pc_argzero no longer scrubs the rq_argp slot, the
shared nlmclnt_lock_event tracepoint class is updated to source
its byte-range fields from lock->fl.fl_start and lock->fl.fl_end,
which both the client and server populate unconditionally; the old
lock_start and lock_len fields are no longer required by the trace.

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