ieee80211_add_athcaps
frm = ieee80211_add_athcaps(frm, bss);
frm = ieee80211_add_athcaps(frm, ni);
ieee80211_add_athcaps(bo->bo_ath, ni);
uint8_t *ieee80211_add_athcaps(uint8_t *, const struct ieee80211_node *);