qlge: Add offload features to vlan interfaces

This patch fills the net_device vlan_features with the proper hardware features,
thus, improving the vlan interface performance.

With the patch applied, I can see around 148% improvement on a TCP_STREAM test,
from 3.5 Gb/s to 8.7 Gb/s. On TCP_RR, I see a 11% improvement, from 18k
to 20. The CPU utilization is almost the same on both cases, from the comparison
above.

Signed-off-by: Breno Leitao <brenohl@br.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>