Increase listen socket backlogs for ssl proxy.

Change-Id: If965b9564d363c58065d05b0d9e1a35bea100422
Reviewed-on: http://review.couchbase.org/36756
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>