nfsd4: rearrange struct nfsd4_slot

Combine two booleans into a single flag field, move the smaller fields
to the end.

(In practice this doesn't make the struct any smaller.  But we'll be
adding another flag here soon.)

Remove some debugging code that doesn't look useful, while we're in the
neighborhood.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>