nfsd defines a type 'encode_dent_fn' which is much like 'filldir_t'
except that the first pointer is 'struct readdir_cd *' rather than
'void *'.  It then casts encode_dent_fn points to 'filldir_t' as
needed.  This hides any other type mismatches between the two such as
the fact that the 'ino' arg recently changed from ino_t to u64.

So: get rid of 'encode_dent_fn', get rid of the cast of the function
type, change the first arg of various functions from 'struct readdir_cd *'
to 'void *', and live with the fact that we have a little less type
checking on the calling of these functions now.
Less internal (to nfsd) checking offset by more external checking, which
is more important.

Thanks to Gabriel Paubert <paubert@iram.es> for discovering this and
providing an initial patch.
Signed-off-by: Gabriel Paubert <paubert@iram.es>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>