net: vrf: remove MTU limits for vrf device

Similiar to commit e94cd811 ("net: remove MTU limits for dummy and
ifb device"), MTU is irrelevant for VRF device. We init it as 64K while
limit it to [68, 1500] may make users feel confused.

Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vrf.c

@@ -1273,6 +1273,9 @@ static void vrf_setup(struct net_device *dev)
 
 	/* default to no qdisc; user can add if desired */
 	dev->priv_flags |= IFF_NO_QUEUE;
+
+	dev->min_mtu = 0;
+	dev->max_mtu = 0;
 }
 
 static int vrf_validate(struct nlattr *tb[], struct nlattr *data[],