ieee802154: Advertize coordinators discovery

Let's introduce the basics for advertizing discovered PANs and
coordinators, which is:
- A new "scan" netlink message group.
- A couple of netlink command/attribute.
- The main netlink helper to send a netlink message with all the
  necessary information to forward the main information to the user.

Two netlink attributes are proactively added to support future UWB
complex channels, but are not actually used yet.

Co-developed-by: David Girault <david.girault@qorvo.com>
Signed-off-by: David Girault <david.girault@qorvo.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20221129135535.532513-2-miquel.raynal@bootlin.com


Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>