NLM: nlm_lookup_file() may return NLMv4-specific error codes

NLM: nlm_lookup_file() may return NLMv4-specific error codes

If the filehandle is stale, or open access is denied for some reason,
nlm_fopen() may return one of the NLMv4-specific error codes nlm4_stale_fh
or nlm4_failed. These get passed right through nlm_lookup_file(),
and so when nlmsvc_retrieve_args() calls the latter, it needs to filter
the result through the cast_status() machinery.

Failure to do so, will trigger the BUG_ON() in encode_nlm_stat...

Signed-off-by: Trond Myklebust <[email protected]>
Reported-by: Larry McVoy <[email protected]>
Cc: [email protected]
Signed-off-by: J. Bruce Fields <[email protected]>