cxgb4/cxgb4vf: Fix up netdev->hw_features

GRO is done by cxgb4/cxgb4vf. Hence set NETIF_F_GRO flag for
both cxgb4/cxgb4vf.
Cleaned up VLAN netdev features in cxgb4vf. Also fixed
NETIF_F_HIGHDMA being set unconditionally for vlan netdev
features.

Signed-off-by: Arjun Vynipadath <arjun@chelsio.com>
Signed-off-by: Vishal Kulkarni <vishal@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>