Feat fake dns address (#902)

Works only with userspace implementation:
1. Configure host to solve DNS requests via a fake DSN server address in the Netbird network.
2. Add to firewall catch rule for these DNS requests.
3. Resolve these DNS requests and respond by writing directly to wireguard device.

iface/device_wrapper.go

@@ -15,6 +15,15 @@ type PacketFilter interface {
 	// DropIncoming filter incoming packets from external sources to host
 	DropIncoming(packetData []byte) bool
 
+	// AddUDPPacketHook calls hook when UDP packet from given direction matched
+	//
+	// Hook function returns flag which indicates should be the matched package dropped or not.
+	// Hook function receives raw network packet data as argument.
+	AddUDPPacketHook(in bool, ip net.IP, dPort uint16, hook func(packet []byte) bool) string
+
+	// RemovePacketHook removes hook by ID
+	RemovePacketHook(hookID string) error
+
 	// SetNetwork of the wireguard interface to which filtering applied
 	SetNetwork(*net.IPNet)
 }
@@ -82,8 +91,8 @@ func (d *DeviceWrapper) Write(bufs [][]byte, offset int) (int, error) {
 	return n, err
 }
 
-// SetFiltering sets packet filter to device
-func (d *DeviceWrapper) SetFiltering(filter PacketFilter) {
+// SetFilter sets packet filter to device
+func (d *DeviceWrapper) SetFilter(filter PacketFilter) {
 	d.mutex.Lock()
 	d.filter = filter
 	d.mutex.Unlock()