net: use core MTU range checking in USB NIC drivers

usbnet:
- Remove stale new_mtu <= 0 check in usbnet.c
- Set min_mtu = 0, max_mtu = 65535 (sub-drivers must set their own
  max_mtu and/or min_mtu as needed)

r8152:
- Set appropriate max_mtu for different variants (1500 or 9194)

lan78xx:
- Set max_mtu = 9000

asix_driver:
- max_mtu = 16384 for ax88178 variant

ax88179:
- max_mtu = 4088

cdc_ncm:
- max_mtu from hardware

cdc-phonet:
- min_mtu = 6, max_mtu = 65541

sierra_net:
- max_mtu = 1500, call usbnet_change_mtu directly
- sierra_net_change_mtu checked for MTU > 1500, then called
  usbnet_change_mtu, but if we set max_mtu to let the network core handle
  the range check, then we can simply call usbnet_change_mtu directly

smsc75xx:
- max_mtu = 9000

CC: netdev@vger.kernel.org
CC: Woojung Huh <woojung.huh@microchip.com>
CC: Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>
CC: Hayes Wang <hayeswang@realtek.com>
CC: Oliver Neukum <oneukum@suse.com>
CC: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 13f033c..c4e748e 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -1980,11 +1980,6 @@
 	int old_rx_urb_size = dev->rx_urb_size;
 	int ret;
 
-	if (new_mtu > MAX_SINGLE_PACKET_SIZE)
-		return -EINVAL;
-
-	if (new_mtu <= 0)
-		return -EINVAL;
 	/* no second zero-length packet read wanted after mtu-sized packets */
 	if ((ll_mtu % dev->maxpacket) == 0)
 		return -EDOM;
@@ -3388,6 +3383,9 @@
 	if (netdev->mtu > (dev->hard_mtu - netdev->hard_header_len))
 		netdev->mtu = dev->hard_mtu - netdev->hard_header_len;
 
+	/* MTU range: 68 - 9000 */
+	netdev->max_mtu = MAX_SINGLE_PACKET_SIZE;
+
 	dev->ep_blkin = (intf->cur_altsetting)->endpoint + 0;
 	dev->ep_blkout = (intf->cur_altsetting)->endpoint + 1;
 	dev->ep_intr = (intf->cur_altsetting)->endpoint + 2;