Mr. GMUgggh this is taking *forever* and it's the first software upgrade of many...
Fumbled through sparse documentation on disparate sources before I found that there is a command to enable a license for the "_shell" command for my new-to-me Mellanox SX6036 switch. Once I had that figured out, I was able to follow along with several guides and get Ethernet enabled instead of the proprietary Infiniband thing. With all of this done, I've changed the default login and then started uploading newer firmware via the web UI.