Instead of open-coding scan parameters (page, channels, duration, etc),
let's use the existing NLA_POLICY* macros. This help greatly reducing
the error handling and clarifying the overall logic.

Fixes: ed3557c9 ("ieee802154: Add support for user scanning requests")
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20230214135035.1202471-2-miquel.raynal@bootlin.comSigned-off-by: Stefan Schmidt <stefan@datenfreihafen.org>