IFM_ISHIFT
ifr.ifr_media = (ifmr->ifm_current & ~IFM_IMASK) | inst << IFM_ISHIFT;
ifmr->ifm_current = (ifmr->ifm_current & ~IFM_IMASK) | inst << IFM_ISHIFT;
#define IFM_INST(x) (((x) & IFM_IMASK) >> IFM_ISHIFT)
((type) | (subtype) | (options) | ((instance) << IFM_ISHIFT))