vdpa/snet: support getting and setting VQ state

This patch adds the get_vq_state and set_vq_state vDPA callbacks.

In order to get the VQ state, the state needs to be read from the DPU.
In order to allow that, the old messaging mechanism is replaced with a new,
flexible control mechanism.
This mechanism allows to read data from the DPU.

The mechanism can be used if the negotiated config version is 2 or
higher.

If the new mechanism is used when the config version is 1, it will call
snet_send_ctrl_msg_old, which is config 1 compatible.

Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
Message-Id: <20230413073337.31367-2-alvaro.karsz@solid-run.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>