net: mac802154: Fix symbol durations

There are two major issues in the logic calculating the symbol durations
based on the page/channel:
- The page number is used in place of the channel value.
- The BIT() macro is missing because we want to check the channel
  value against a bitmask.

Fix these two errors and apologize loudly for this mistake.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20220428164140.251965-1-miquel.raynal@bootlin.com


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