mac802154: add default interface registration

This patch adds a default interface registration for a wpan interface
type. Currently the 802.15.4 subsystem need to call userspace tools to
add an interface. This patch is like mac80211 handling for registration
a station interface type by default.

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