virtio-net: alloc big buffers also when guest can receive UFO

virtio-net: alloc big buffers also when guest can receive UFO

We should alloc big buffers also when guest can receive UFO
packets to let the big packets fit into guest rx buffer.

Fixes 5d2cb905101a959be3aeddd8d4fd37c146371e6c
(virtio-net: Allow UFO feature to be set and advertised.)

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>