Don't check interface of inbound message if interfaces are not filtered

We don't have a proper kernel-net interface on Android yet, so the check
for a usable interface does not work there.

src/libcharon/network/receiver.c

@@ -447,8 +447,9 @@ static job_requeue_t receive_packets(private_receiver_t *this)
 
 	dst = packet->get_destination(packet);
 	src = packet->get_source(packet);
-	if (!hydra->kernel_interface->get_interface(hydra->kernel_interface,
+	if (!hydra->kernel_interface->all_interfaces_usable(hydra->kernel_interface)
-												dst, NULL))
+		&& !hydra->kernel_interface->get_interface(hydra->kernel_interface,
+												   dst, NULL))
 	{
 		DBG3(DBG_NET, "received packet from %#H to %#H on ignored interface",
 			 src, dst);

src/libhydra/kernel/kernel_interface.c

@@ -389,6 +389,12 @@ METHOD(kernel_interface_t, is_interface_usable, bool,
 										   NULL, iface) == expected;
 }
 
+METHOD(kernel_interface_t, all_interfaces_usable, bool,
+	private_kernel_interface_t *this)
+{
+	return this->ifaces_filter == NULL;
+}
+
 METHOD(kernel_interface_t, get_address_by_ts, status_t,
 	private_kernel_interface_t *this, traffic_selector_t *ts, host_t **ip)
 {
@@ -698,6 +704,7 @@ kernel_interface_t *kernel_interface_create()
 			.enable_udp_decap = _enable_udp_decap,
 
 			.is_interface_usable = _is_interface_usable,
+			.all_interfaces_usable = _all_interfaces_usable,
 			.get_address_by_ts = _get_address_by_ts,
 			.add_ipsec_interface = _add_ipsec_interface,
 			.remove_ipsec_interface = _remove_ipsec_interface,
@@ -725,12 +732,9 @@ kernel_interface_t *kernel_interface_create()
 					"%s.interfaces_use", NULL, hydra->daemon);
 	if (!ifaces)
 	{
+		this->ifaces_exclude = TRUE;
 		ifaces = lib->settings->get_str(lib->settings,
 					"%s.interfaces_ignore", NULL, hydra->daemon);
-		if (ifaces)
-		{
-			this->ifaces_exclude = TRUE;
-		}
 	}
 	if (ifaces)
 	{

src/libhydra/kernel/kernel_interface.h

@@ -312,7 +312,7 @@ struct kernel_interface_t {
 	 * @param name			allocated interface name (optional)
 	 * @return				TRUE if interface found and usable
 	 */
-	bool (*get_interface) (kernel_interface_t *this, host_t *host, char **name);
+	bool (*get_interface)(kernel_interface_t *this, host_t *host, char **name);
 
 	/**
 	 * Creates an enumerator over all local addresses.
@@ -415,6 +415,13 @@ struct kernel_interface_t {
 	 */
 	bool (*is_interface_usable)(kernel_interface_t *this, const char *iface);
 
+	/**
+	 * Check if interfaces are excluded by config.
+	 *
+	 * @return				TRUE if no interfaces are exclued by config
+	 */
+	bool (*all_interfaces_usable)(kernel_interface_t *this);
+
 	/**
 	 * Tries to find an IP address of a local interface that is included in the
 	 * supplied traffic selector.