staging: vt6655: Remove unnecessary condition around include

ethtool (and SIOCETHTOOL in particular) is part of Linux since the
pre-git era, it thus makes no sense no sense to make the include of
linux/ethtool.h conditional. Also remove the unused define
DEVICE_ETHTOOL_IOCTL_SUPPORT.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>