Feat linux firewall support (#805)

Update the client's engine to apply firewall rules received from the manager (results of ACL policy).

iface/iface.go

@@ -1,6 +1,7 @@
 package iface
 
 import (
+	"fmt"
 	"net"
 	"sync"
 	"time"
@@ -118,3 +119,17 @@ func (w *WGIface) Close() error {
 	defer w.mu.Unlock()
 	return w.tun.Close()
 }
+
+// SetFiltering sets packet filters for the userspace impelemntation
+func (w *WGIface) SetFiltering(filter PacketFilter) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	if w.tun.wrapper == nil {
+		return fmt.Errorf("userspace packet filtering not handled on this device")
+	}
+
+	filter.SetNetwork(w.tun.address.Network)
+	w.tun.wrapper.SetFiltering(filter)
+	return nil
+}