wpi_free_rbuf
MEXTADD(mnew, rbuf->vaddr, WPI_RBUF_SIZE, 0, wpi_free_rbuf,
MEXTADD(data->m, rbuf->vaddr, WPI_RBUF_SIZE, 0, wpi_free_rbuf,
static void wpi_free_rbuf(struct mbuf *, void *, size_t, void *);