net: dsa: microchip: ksz8795: Correctly handle huge frame configuration

Because of the logic in place, SW_HUGE_PACKET can never be set.
(If the first condition is true, then the 2nd one is also true, but is not
executed)

Change the logic and update each bit individually.

Fixes: 29d1e85f

 ("net: dsa: microchip: ksz8: add MTU configuration support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/43107d9e8b5b8b05f0cbd4e1f47a2bb88c8747b2.1681755535.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Jakub Kicinski <kuba@kernel.org>