Use Data::Data only with Host AP driver; mac80211 can use Data::Nullfunc

The inactivity poll was originally supposed to use Data::Nullfunc, but
due to Prism2/2.5/3 firmware issues, this was changed to an empty
Data::Data frame. mac80211 does not have such an issue, so change the
inactivity poll frame to be Data::Nullfunc by default and use the
Data::Data workaround only with Host AP driver.

hostapd/sta_info.c

@@ -288,12 +288,23 @@ void ap_handle_timer(void *eloop_ctx, void *timeout_ctx)
 		sta->flags |= WLAN_STA_PENDING_POLL;
 
 #ifndef CONFIG_NATIVE_WINDOWS
-		/* FIX: WLAN_FC_STYPE_NULLFUNC would be more appropriate, but
-		 * it is apparently not retried so TX Exc events are not
-		 * received for it */
 		os_memset(&hdr, 0, sizeof(hdr));
-		hdr.frame_control =
-			IEEE80211_FC(WLAN_FC_TYPE_DATA, WLAN_FC_STYPE_DATA);
+		if (hapd->driver &&
+		    os_strcmp(hapd->driver->name, "hostap") == 0) {
+			/*
+			 * WLAN_FC_STYPE_NULLFUNC would be more appropriate,
+			 * but it is apparently not retried so TX Exc events
+			 * are not received for it.
+			 */
+			hdr.frame_control =
+				IEEE80211_FC(WLAN_FC_TYPE_DATA,
+					     WLAN_FC_STYPE_DATA);
+		} else {
+			hdr.frame_control =
+				IEEE80211_FC(WLAN_FC_TYPE_DATA,
+					     WLAN_FC_STYPE_NULLFUNC);
+		}
+
 		hdr.frame_control |= host_to_le16(WLAN_FC_FROMDS);
 		os_memcpy(hdr.IEEE80211_DA_FROMDS, sta->addr, ETH_ALEN);
 		os_memcpy(hdr.IEEE80211_BSSID_FROMDS, hapd->own_addr,