The extlen of a upr del/exp is 18 bytes not 30

Change-Id: Iac9e1299458fc5f195408f32679d18f478f6a15d
Reviewed-on: http://review.couchbase.org/32705
Reviewed-by: Artem Stemkovski <artem@couchbase.com>
Tested-by: Artem Stemkovski <artem@couchbase.com>