macvlan: use netdev_is_rx_handler_busy instead of checking specific type

netdev_is_rx_handler_busy() check is a superset of netif_is_ipvlan_port()
check and hence should be preferred.

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>