net: vrf: Update flags and features settings

1. Default VRF devices to not having a qdisc (IFF_NO_QUEUE). Users
   can add one as desired.

2. Disable adding a VLAN to a VRF device.

3. Enable offloads and hardware features similar to other logical
   devices (e.g., dummy, veth)

Change provides a significant boost in TCP stream Tx performance,
from ~2,700 Mbps to ~18,100 Mbps and makes throughput close to the
performance without a VRF (18,500 Mbps). netperf TCP_STREAM benchmark
using qemu with virtio+vhost for the NICs

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>