netdev: restore MTU change operation

alloc_etherdev() used to install a default implementation of this
operation, but it must now be explicitly installed in struct
net_device_ops.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/8139too.c b/drivers/net/8139too.c
index 8ae72ec..0e2ba21 100644
--- a/drivers/net/8139too.c
+++ b/drivers/net/8139too.c
@@ -908,6 +908,7 @@
 	.ndo_open		= rtl8139_open,
 	.ndo_stop		= rtl8139_close,
 	.ndo_get_stats		= rtl8139_get_stats,
+	.ndo_change_mtu		= eth_change_mtu,
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_set_mac_address 	= rtl8139_set_mac_address,
 	.ndo_start_xmit		= rtl8139_start_xmit,