bwn_dma_freeslot
bwn_dma_freeslot(dr) < BWN_TX_SLOTS_PER_FRAME) {
static int bwn_dma_freeslot(struct bwn_dma_ring *);
KASSERT(bwn_dma_freeslot(dr) >= BWN_TX_SLOTS_PER_FRAME,
KASSERT(bwn_dma_freeslot(dr) != 0, ("%s:%d: fail", __func__, __LINE__));