various minor NFSv4.2 review comments

FYI: the version you commited mentions sr_allocated in the text,
but it's gone from the XDR.  Also READ_PLUS now reports the allocation
status for a hole, which nothing else does.  Is that intended?

If not something like this should clean up the remaining reservation
bits:

Signed-off-by: Tom Haynes <Thomas.Haynes@primarydata.com>