mac802154: remove unused hw_filt attribute

This patch removed an attribute from ieee802154_hw structure which is
never used inside kernel. Address information are stored inside wpan_dev
nowadays.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reviewed-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>