nm_kr_rxspace
int t = na->num_rx_desc - 1 - nm_kr_rxspace(kring);
max_avail = n - 1 - nm_kr_rxspace(na->rx_rings[0]);
num = na->num_rx_desc - 1 - nm_kr_rxspace(kring);
#define nm_kr_txspace(_k) nm_kr_rxspace(_k)
n = kring->nkr_num_slots - nm_kr_rxspace(kring);