vdpa: Add SetSteeringEBPF method for NetClientState

vdpa: Add SetSteeringEBPF method for NetClientState

At present, to enable the VIRTIO_NET_F_RSS feature, eBPF must
be loaded for the vhost backend.

Given that vhost-vdpa is one of the vhost backend, we need to
implement the SetSteeringEBPF method to support RSS for vhost-vdpa,
even if vhost-vdpa calculates the rss hash in the hardware device
instead of in the kernel by eBPF.

Although this requires QEMU to be compiled with `--enable-bpf`
configuration even if the vdpa device does not use eBPF to
calculate the rss hash, this can avoid adding the specific
conditional statements for vDPA case to enable the VIRTIO_NET_F_RSS
feature, which reduces code maintainbility.

Suggested-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
Message-Id: <280e20ddce55b6de60f1552ba0865bffffe909b2.1698195059.git.yin31149@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>