netmap_vp_reg
netmap_vp_reg(na, onoff);
netmap_vp_reg(&hostna->up, onoff);
int netmap_vp_reg(struct netmap_adapter *na, int onoff);
na->nm_register = netmap_vp_reg; /* use the one provided by bdg */
if (!NM_NA_VALID(ifp) || NA(ifp)->nm_register != netmap_vp_reg) {