mac802154: rx: monitor receive cleanup

This patch replace the !netif_running(sdata->dev) instead we doing a
!ieee802154_sdata_running(sdata). Also move this in two separate if
branches to compare with mac80211 code.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>