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/cdc-phonet.c b/drivers/net/usb/cdc-phonet.c
index ff2270e..eb52de8 100644
--- a/drivers/net/usb/cdc-phonet.c
+++ b/drivers/net/usb/cdc-phonet.c
@@ -276,21 +276,11 @@ static int usbpn_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 	return -ENOIOCTLCMD;
 }
 
-static int usbpn_set_mtu(struct net_device *dev, int new_mtu)
-{
-	if ((new_mtu < PHONET_MIN_MTU) || (new_mtu > PHONET_MAX_MTU))
-		return -EINVAL;
-
-	dev->mtu = new_mtu;
-	return 0;
-}
-
 static const struct net_device_ops usbpn_ops = {
 	.ndo_open	= usbpn_open,
 	.ndo_stop	= usbpn_close,
 	.ndo_start_xmit = usbpn_xmit,
 	.ndo_do_ioctl	= usbpn_ioctl,
-	.ndo_change_mtu = usbpn_set_mtu,
 };
 
 static void usbpn_setup(struct net_device *dev)
@@ -301,6 +291,8 @@ static void usbpn_setup(struct net_device *dev)
 	dev->type		= ARPHRD_PHONET;
 	dev->flags		= IFF_POINTOPOINT | IFF_NOARP;
 	dev->mtu		= PHONET_MAX_MTU;
+	dev->min_mtu		= PHONET_MIN_MTU;
+	dev->max_mtu		= PHONET_MAX_MTU;
 	dev->hard_header_len	= 1;
 	dev->dev_addr[0]	= PN_MEDIA_USB;
 	dev->addr_len		= 1;