lockd: Use xdrgen XDR functions for the NLMv4 FREE_ALL procedure

lockd: Use xdrgen XDR functions for the NLMv4 FREE_ALL procedure

With all other NLMv4 procedures now converted to xdrgen-generated
XDR functions, the FREE_ALL procedure can be converted as well.
This conversion allows the removal of nlm4svc_retrieve_args(),
a 79-line helper function that was used only by FREE_ALL to
retrieve client information from lockd's internal data
structures.

Replace the NLMPROC4_FREE_ALL entry in the nlm_procedures4
array with an entry that uses xdrgen-built XDR decoders and
encoders. The procedure handler is updated to use the new
wrapper structure (nlm4_notify_wrapper) and call
nlm4svc_lookup_host() directly, eliminating the need for the
now-removed helper function.

The .pc_argzero field is set to zero because xdrgen decoders
fully initialize all fields in argp->xdrgen, making the early
defensive memset unnecessary. The remaining argp fields that
fall outside the xdrgen structures are cleared explicitly as
needed.

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