WNM: Additional BSS Transition Management capability

Add some more functionality for BSS Transition Management:
- advertise support for BSS Transition Management in extended
  capabilities element
- add hostapd.conf parameter bss_transition=1 for enabling support
  for BSS Transition Management
- add "hostapd_cli disassoc_imminent <STA> <num TBTTs>" for sending
  disassociation imminent notifications for testing purposes
- wpa_supplicant: trigger a new scan to find another BSS if the
  current AP indicates disassociation imminent (TODO: the old AP needs
  to be marked to use lower priority to avoid re-selecting it)

Signed-hostap: Jouni Malinen <j@w1.fi>

src/ap/ap_config.h

@@ -392,6 +392,7 @@ struct hostapd_bss_config {
 	int time_advertisement;
 	char *time_zone;
 	int wnm_sleep_mode;
+	int bss_transition;
 
 	/* IEEE 802.11u - Interworking */
 	int interworking;

src/ap/ieee802_11_shared.c

@@ -192,6 +192,8 @@ u8 * hostapd_eid_ext_capab(struct hostapd_data *hapd, u8 *eid)
 	*pos = 0x00;
 	if (hapd->conf->wnm_sleep_mode)
 		*pos |= 0x02; /* Bit 17 - WNM-Sleep Mode */
+	if (hapd->conf->bss_transition)
+		*pos |= 0x08; /* Bit 19 - BSS Transition */
 	pos++;
 
 	if (len < 4)

src/ap/wnm_ap.c

@@ -250,6 +250,15 @@ int ieee802_11_rx_wnm_action_ap(struct hostapd_data *hapd,
 		return -1;
 
 	switch (action->data[0]) {
+	case WNM_BSS_TRANS_MGMT_QUERY:
+		wpa_printf(MSG_DEBUG, "WNM: BSS Transition Management Query");
+		/* TODO */
+		return -1;
+	case WNM_BSS_TRANS_MGMT_RESP:
+		wpa_printf(MSG_DEBUG, "WNM: BSS Transition Management "
+			   "Response");
+		/* TODO */
+		return -1;
 	case WNM_SLEEP_MODE_REQ:
 		ieee802_11_rx_wnmsleep_req(hapd, action->sa, action->data + 1,
 					   action->len - 1);

src/common/ieee802_11_defs.h

@@ -538,6 +538,16 @@ struct ieee80211_mgmt {
 					 * Entries */
 					u8 variable[0];
 				} STRUCT_PACKED bss_tm_req;
+				struct {
+					u8 action; /* 8 */
+					u8 dialog_token;
+					u8 status_code;
+					u8 bss_termination_delay;
+					/* Target BSSID (optional),
+					 * BSS Transition Candidate List
+					 * Entries (optional) */
+					u8 variable[0];
+				} STRUCT_PACKED bss_tm_resp;
 			} u;
 		} STRUCT_PACKED action;
 	} u;