'Attach an interface and set its port'

def attach(self, intf):

    port = self.ports[intf]
    if port:
        if self.isOldOVS():
            self.cmd('ovs-vsctl    add-port', self, intf)
        else:
            self.cmd('ovs-vsctl    add-port', self, intf, '--    set    Interface', intf, ('ofport_request=%s' % port))
        self.validatePort(intf)
