Do not continually reschedule specific scans to help finding hidden SSIDs

In situations where the driver does background scanning and sends a
steady stream of scan results, wpa_supplicant would continually
reschedule the scan.  This resulted in specific SSID scans never
happening for a hidden AP, and the supplicant never connecting to the AP
because it never got found.  Instead, if there's an already scheduled
scan, and a request comes in to reschedule it, and there are enabled
scan_ssid=1 network blocks, let the scan happen anyway so the hidden
SSID has a chance to be found.

src/utils/eloop.c

@@ -315,6 +315,25 @@ int eloop_cancel_timeout(eloop_timeout_handler handler,
 }
 
 
+int eloop_is_timeout_registered(eloop_timeout_handler handler,
+				void *eloop_data, void *user_data)
+{
+	struct eloop_timeout *tmp;
+
+	tmp = eloop.timeout;
+	while (tmp != NULL) {
+		if (tmp->handler == handler &&
+		    tmp->eloop_data == eloop_data &&
+		    tmp->user_data == user_data)
+			return 1;
+
+		tmp = tmp->next;
+	}
+
+	return 0;
+}
+
+
 #ifndef CONFIG_NATIVE_WINDOWS
 static void eloop_handle_alarm(int sig)
 {