mcreq_dup_packet: always declare STANDALONE_SPAN for values

Previously we were only doing this for non-inflated values. This is a
logic error.

Change-Id: I09357fbdca32d550c5435ff209f80fe5a747df33
Reviewed-on: http://review.couchbase.org/38190
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>