DCP expiries of xattr items appearing as deletions

Both PyDCP and Wireshark report that when streaming expired items with xattr's without using the xattr flag, some appear as deletions while some retain the expiry opcode.

Method to replicate:

• Insert n items with xattr's
• Touch each item with an expiry time
• Wait/sleep past the expiry time
• Get/lookup each item to trigger expiration of that item
• Start a DCP stream without the xattr flag
• DCP control the enable expiry opcodes on
• You'll get a mix of deletions and expirations.

If you stream with the xattr flag on, you'd get all expirations. Also, the stat for expired documents (vb_active_expired) is correct so it appears that the items are being expired correctly.

As far as I can tell, the opcode for the same key is not guaranteed to be the same on repeated DCP stream attempts (without changing the items) which is definitely not expected behaviour. I have managed to manually demonstrate this on both couchbase and ephemeral buckets.