mac802154: fix time calculation in ieee802154_configure_durations()

Since 'symbol_duration' of 'struct wpan_phy' is in nanoseconds but
'lifs_period' and 'sifs_period' are both in microseconds, fix time
calculation in 'ieee802154_configure_durations()' and use convenient
'NSEC_PER_USEC' in 'ieee802154_setup_wpan_phy_pib()' as well.
Compile tested only.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 781830c8

 ("net: mac802154: Set durations automatically")
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Message-ID: <20240508114010.219527-1-dmantipov@yandex.ru>
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>