vp_vdpa: support feature provisioning

vp_vdpa: support feature provisioning

This patch allows the device features to be provisioned via
netlink. This is done by:

1) validating the provisioned features to be a subset of the parent
   features.
2) clearing the features that is not wanted by the userspace

For example:

# vdpa mgmtdev show
pci/0000:02:00.0:
  supported_classes net
  max_supported_vqs 3
  dev_features CSUM GUEST_CSUM CTRL_GUEST_OFFLOADS MAC GUEST_TSO4
  GUEST_TSO6 GUEST_ECN GUEST_UFO HOST_TSO4 HOST_TSO6 HOST_ECN HOST_UFO
  MRG_RXBUF STATUS CTRL_VQ CTRL_RX CTRL_VLAN CTRL_RX_EXTRA
  GUEST_ANNOUNCE CTRL_MAC_ADDR RING_INDIRECT_DESC RING_EVENT_IDX
  VERSION_1 ACCESS_PLATFORM

1) provision vDPA device with all features that are supported by the virtio-pci

# vdpa dev add name dev1 mgmtdev pci/0000:02:00.0
# vdpa dev config show
dev1: mac 52:54:00:12:34:56 link up link_announce false mtu 65535
  negotiated_features CSUM GUEST_CSUM CTRL_GUEST_OFFLOADS MAC
  GUEST_TSO4 GUEST_TSO6 GUEST_ECN GUEST_UFO HOST_TSO4 HOST_TSO6
  HOST_ECN HOST_UFO MRG_RXBUF STATUS CTRL_VQ CTRL_RX CTRL_VLAN
  GUEST_ANNOUNCE CTRL_MAC_ADDR RING_INDIRECT_DESC RING_EVENT_IDX
  VERSION_1 ACCESS_PLATFORM

2) provision vDPA device with a subset of the features

# vdpa dev add name dev1 mgmtdev pci/0000:02:00.0 device_features 0x300020000
# dev1: mac 52:54:00:12:34:56 link up link_announce false mtu 65535
  negotiated_features CTRL_VQ VERSION_1 ACCESS_PLATFORM

Reviewed-by: Eli Cohen <elic@nvidia.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220927074810.28627-4-jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>