[NET]: ethtool ops are the only way

During the transition to the ethtool_ops way of doing things, we supported
calling the device's ->do_ioctl method to allow unconverted drivers to
continue working.  Those days are long behind us, all in-tree drivers
use the ethtool_ops way, and so we no longer need to support this.

The bonding driver is the biggest beneficiary of this; it no longer
needs to call ioctl() as a fallback if ethtool_ops aren't supported.

Also put a proper copyright statement on ethtool.c.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: David S. Miller <davem@davemloft.net>