Ex:
        add(dst="2001:db8:cafe:f000::/56")
        add(dst="2001:db8:cafe:f000::/56", gw="2001:db8:cafe::1")
        add(dst="2001:db8:cafe:f000::/64", gw="2001:db8:cafe::1", dev="eth0")

def add(self, *args, **kargs):
        """Ex:
        add(dst="2001:db8:cafe:f000::/56")
        add(dst="2001:db8:cafe:f000::/56", gw="2001:db8:cafe::1")
        add(dst="2001:db8:cafe:f000::/64", gw="2001:db8:cafe::1", dev="eth0")
        """
        self.invalidate_cache()
        self.routes.append(self.make_route(*args, **kargs))