lockd: Use xdrgen XDR functions for the NLMv3 FREE_ALL procedure

lockd: Use xdrgen XDR functions for the NLMv3 FREE_ALL procedure

With all other NLMv3 procedures now converted to xdrgen-generated
XDR functions, the FREE_ALL procedure can be converted as well.
This conversion allows the removal of nlmsvc_retrieve_args(),
a 52-line helper function that was used only by FREE_ALL to
retrieve client information from lockd's internal data
structures.

Replace the NLMPROC_FREE_ALL entry in the nlmsvc_procedures
array with an entry that uses xdrgen-built XDR decoders and
encoders. The procedure handler is updated to use the new
wrapper structure (nlm_notify_wrapper) and call
nlm3svc_lookup_host() directly, eliminating the need for the
now-removed helper function.

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
nlm_notify_wrapper structure has no members beyond the xdrgen
substructure, so no further initialization is required.

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