NETMAP_NO_TX_POLL
if (nmr->nr_ringid & NETMAP_NO_TX_POLL) {
d->req.nr_ringid |= new_flags & (NETMAP_NO_TX_POLL | NETMAP_DO_RX_POLL);
t->nmd->reg.nr_flags |= NETMAP_NO_TX_POLL;
priv->nmd = nm_open(priv->ifname, NULL, NETMAP_NO_TX_POLL, NULL);