ehea: Add GRO support

Add GRO support to the ehea driver.

v3:
[cascardo] no need to enable GRO, since it's enabled by default
[cascardo] vgrp was removed in the vlan cleanup

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>