Staging: w35und: convert code to use ETH_ALEN

As suggested by Harvey Harrison, convert driver to use ETH_ALEN and kill a
private macro from common.h that is used for the same thing.

Acked-by: Harvey Harrison <harvey.harrison@gmail.com>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>