vDPA/ifcvf: support userspace to query features and MQ of a management device

Adapting to current netlink interfaces, this commit allows userspace
to query feature bits and MQ capability of a management device.

Currently both the vDPA device and the management device are the VF itself,
thus this ifcvf should initialize the virtio capabilities in probe() before
setting up the struct vdpa_mgmt_dev.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Message-Id: <20220722115309.82746-3-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>