Support packet filtering for VPCS

https://github.com/GNS3/gns3-gui/issues/765

gns3server/compute/vpcs/vpcs_vm.py

@@ -73,6 +73,10 @@ class VPCSVM(BaseNode):
             self.startup_script = startup_script
         self._ethernet_adapter = EthernetAdapter()  # one adapter with 1 Ethernet interface
 
+    @property
+    def ethernet_adapter(self):
+        return self._ethernet_adapter
+
     @asyncio.coroutine
     def close(self):
         """
@@ -387,6 +391,16 @@ class VPCSVM(BaseNode):
 
         return nio
 
+    @asyncio.coroutine
+    def port_update_nio_binding(self, port_number, nio):
+        if not self._ethernet_adapter.port_exists(port_number):
+            raise VPCSError("Port {port_number} doesn't exist in adapter {adapter}".format(adapter=self._ethernet_adapter,
+                                                                                           port_number=port_number))
+        if self.ubridge:
+            yield from self._update_ubridge_udp_connection("VPCS-{}".format(self._id), self._local_udp_tunnel[1], nio)
+        elif self.is_running():
+            raise VPCSError("Sorry, adding a link to a started VPCS instance is not supported without using uBridge.")
+
     @asyncio.coroutine
     def port_remove_nio_binding(self, port_number):
         """