[U-Boot] How to disable MAC address for usb_ether

Hi,

My board has one Ethernet, one USB Host and one USB Slave.

Command bdinfo shows below:

eth0name = cpsw ethaddr = 90:59:af:54:1a:28 eth1name = usb_ether eth1addr = 90:59:af:54:1a:2a current eth = cpsw

Would you please teach me how to disable usb_ether MAC address, thus bdinfo will show "eth1addr = (not set)"?

Thanks a lot.