ehea: Add vlan_features

We weren't enabling any VLAN features so we missed out on checksum
offload and TSO when using VLANs. Enable them.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>