Get rid of direct hostapd_for_each_interface() calls

src/ap/*.c must not call functions in hostapd or wpa_supplicant
directories directly, so avoid this by using a callback function
pointer.

wpa_supplicant/ap.c

@@ -34,21 +34,6 @@
 #include "ap.h"
 
 
-struct hapd_interfaces {
-	size_t count;
-	struct hostapd_iface **iface;
-};
-
-
-int hostapd_for_each_interface(struct hapd_interfaces *interfaces,
-			       int (*cb)(struct hostapd_iface *iface,
-					 void *ctx), void *ctx)
-{
-	/* TODO */
-	return 0;
-}
-
-
 static int wpa_supplicant_conf_ap(struct wpa_supplicant *wpa_s,
 				  struct wpa_ssid *ssid,
 				  struct hostapd_config *conf)