NCBC-556: SslConnection uses obsolete GetBuffer method - throws NIE

Change-Id: I44fa6e43c9b606f83789c6258c75f6a0c623d98d
Reviewed-on: http://review.couchbase.org/39648
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Brett Lawson <brett19@gmail.com>