Fix hostapd operation without hw_mode driver data

Commit 7f0303d5b0bb425f3e7318a7016b55ba9e67f9de ('hostapd: Verify VHT
160/80+80 MHz driver support') added couple of hapd->iface->current_mode
dereferences of which the one in hostapd_set_freq() can be hit with some
configuration files when using driver wrappers that do not have hw_mode
data, i.e., when current_mode is NULL. This could result in segmentation
fault when trying to use driver=wired. Fix this by checking that
current_mode is not NULL before dereferencing it to get vht_capab.

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

src/ap/ap_drv_ops.c

@@ -573,7 +573,8 @@ int hostapd_set_freq(struct hostapd_data *hapd, int mode, int freq,
 				    vht_enabled, sec_channel_offset,
 				    vht_oper_chwidth,
 				    center_segment0, center_segment1,
-				    hapd->iface->current_mode->vht_capab))
+				    hapd->iface->current_mode ?
+				    hapd->iface->current_mode->vht_capab : 0))
 		return -1;
 
 	if (hapd->driver == NULL)