vtnet_txq_encap
static int vtnet_txq_encap(struct vtnet_txq *, struct mbuf **, int);
if (vtnet_txq_encap(txq, &m0, M_NOWAIT) != 0) {
if (vtnet_txq_encap(txq, &m, M_NOWAIT) != 0) {
error = vtnet_txq_encap(txq, &m, M_NOWAIT | M_USE_RESERVE);