Delete Open vSwitch flows matching the nic port

When two users instantiate a VM template, they both get the same IP, so
the same MAC address, in their own respective networks differenciated by
VLAN ID.

When one of them delete her VM, the flow is removed for the other VM too
since the flows are selected only by matching MAC address.

* src/vnm_mad/remotes/ovswitch/OpenvSwitch.rb (OpenvSwitchVLAN#deactivate):
  Delet flows on the nic port matching the MAC address, take care of
  nonexistent port.

* src/vnm_mad/remotes/ovswitch/OpenvSwitch.rb (OpenvSwitchVLAN#del_flows):
  Remove useless function.

src/vnm_mad/remotes/ovswitch/OpenvSwitch.rb

@@ -75,8 +75,9 @@ def deactivate
         process do |nic|
             @nic = nic
 
-            # Remove flows
-            del_flows
+            # Remove flows on the nic port if it exists
+            in_port = port
+            del_flow "in_port=#{in_port},dl_src=#{@nic[:mac]}" if not in_port.nil?
         end
 
         unlock
@@ -156,22 +157,6 @@ def configure_fw
         end
     end
 
-    def del_flows
-        in_port = ""
-
-        dump_flows = "#{command(:ovs_ofctl)} dump-flows #{@nic[:bridge]}"
-        `#{dump_flows}`.lines do |flow|
-            next unless flow.match("#{@nic[:mac]}")
-            flow = flow.split.select{|e| e.match(@nic[:mac])}.first
-            if in_port.empty? and (m = flow.match(/in_port=(\d+)/))
-                in_port = m[1]
-            end
-            del_flow flow
-        end
-
-        del_flow "in_port=#{in_port}" if !in_port.empty?
-    end
-
     def add_flow(filter,action,priority=nil)
         priority = (priority.to_s.empty? ? "" : "priority=#{priority},")
 
@@ -195,6 +180,9 @@ def port
         dump_ports = `#{command(:ovs_ofctl)} \
                       dump-ports #{@nic[:bridge]} #{@nic[:tap]}`
 
+        # Do not return 1 if no port is associated with the interface
+        return nil if dump_ports.empty?
+
         @nic[:port] = dump_ports.scan(/^\s*port\s*(\d+):/).flatten.first
     end