IEEE80211_DUR_DS_SLOT
ifst = __SHIFTIN(IEEE80211_DUR_DS_SLOT, ATW_IFST_SLOT_MASK) |
#define IEEE80211_DUR_DS_PIFS (IEEE80211_DUR_DS_SIFS + IEEE80211_DUR_DS_SLOT)
2 * IEEE80211_DUR_DS_SLOT)