Update download link for copy offload tool

This patch updates the download link for the NetApp NFS Copy Offload
tool, which has moved from the NetApp community page to the NetApp
support portal.

Change-Id: Ifd509d06b8288db5e445e7d0eee885c433a734b4
backport: icehouse
(cherry picked from commit 5d88e2f3efdf79f32a22f857bab437aba3491708)