Moved the setting of extlen to inside the raw_command
to ensure the memcpy starts at the correct address.

Change-Id: I16f3077991389686fc2831543ce6962bfde7dd9d
Reviewed-on: http://review.couchbase.org/42517
Tested-by: Daniel Owen <owend@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>