ieee802154: Change error code on monitor scan netlink request

Returning EPERM gives the impression that "right now" it is not
possible, but "later" it could be, while what we want to express is the
fact that this is not currently supported at all (might change in the
future). So let's return EOPNOTSUPP instead.

Fixes: ed3557c9 ("ieee802154: Add support for user scanning requests")
Suggested-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20230214135035.1202471-4-miquel.raynal@bootlin.com


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