MB-12288:only allow xdcr-over-ssl proxying to memcached data port

Change-Id: Ied0f2c8e9d01959ca5be34b15b2b47d91d89cac8
Reviewed-on: http://review.couchbase.org/41804
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>