Fix AP build without NEED_AP_MLME

Commit 1b487b8b1e95e1fbd9e00d52d883ba0ac4c2e4bf added CH_SWITCH
event for nl80211, but ended up using hostapd_hw_get_channel()
regardless of build configuration for driver interfaces. This
function is not always available, so make its use conditional
on NEED_AP_MLME.

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

src/ap/drv_callbacks.c

@@ -277,6 +277,7 @@ void hostapd_event_sta_low_ack(struct hostapd_data *hapd, const u8 *addr)
 void hostapd_event_ch_switch(struct hostapd_data *hapd, int freq, int ht,
 			     int offset)
 {
+#ifdef NEED_AP_MLME
 	int channel;
 
 	hostapd_logger(hapd, NULL, HOSTAPD_MODULE_IEEE80211,
@@ -296,6 +297,7 @@ void hostapd_event_ch_switch(struct hostapd_data *hapd, int freq, int ht,
 	hapd->iconf->channel = channel;
 	hapd->iconf->ieee80211n = ht;
 	hapd->iconf->secondary_channel = offset;
+#endif /* NEED_AP_MLME */
 }