Right, that makes sense.
Your switch is in InfiniBand mode only.
You need to install the Ethernet license to be able to convert ports from InfiniBand to Ethernet.
# license install <license key>
Once you do that, you will need to change the system profile to Ethernet or VPI (allow InfiniBand and Ethernet).
switch (config) system profile eth-single-switch or
switch (config) system profile vpi-single-switch (if you need both InfiniBand ports and Ethernet ports)
reboot the switch. and you should be good.
to get the license you need to contact the Mellanox sales or Mellanox support.
I suggest you also get the User Manual, see Where can I find the MLNX-OS User Manual
Thanks,
Ophir.