MCX416A-GCAT is a dual port card , can you try connecting the cable in loop back (from port 1 to port 2) and check if there is a link?
Are the hosts connected directly or via a switch ? if it is a switch what is the switch type?
There was a link when I tried looping the cable from port 1 to port 2. However, I've contacted Mellanox support and this was their response: "Mellanox Adapter card do not support splitting their ports.
You can split a Mellanox Switch port into 4x or 2x only."
So It looks like the card that I have will not work with MCP7H00-G003.