MB-11642: Change the priority based on the type of dcp connection

Change-Id: I1b9a6846879385308bee3920bfa182fc41e39b4f
Reviewed-on: http://review.couchbase.org/41758
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>