Use ntohll and htonll from libplatform

Change-Id: I182e88f26ab833b2568c478b3f37204208ecc6b9
Reviewed-on: http://review.couchbase.org/30954
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>