USB: Gadget Ethernet: Re-enable Jumbo frames.

Fixes: <b3e3893e> ("net: use core MTU range checking")
which patched only one of two functions used to setup the
USB Gadget Ethernet driver, causing a serious performance
regression in the ability to increase mtu size above 1500.
Signed-off-by: John Greb <h3x4m3r0n@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/function/u_ether.c

@@ -844,6 +844,10 @@ struct net_device *gether_setup_name_default(const char *netname)
 	net->ethtool_ops = &ops;
 	SET_NETDEV_DEVTYPE(net, &gadget_type);
 
+	/* MTU range: 14 - 15412 */
+	net->min_mtu = ETH_HLEN;
+	net->max_mtu = GETHER_MAX_ETH_FRAME_LEN;
+
 	return net;
 }
 EXPORT_SYMBOL_GPL(gether_setup_name_default);