net: ethoc: remove ethoc_config

ethoc_config() returns -ENOSYS and does not implement anything useful,
let's remove it such that net/core/dev_ioctl.c::dev_ifsioc can return
something meaningful like -EOPNOTSUPP.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>