libvhost-user: mask F_INFLIGHT_SHMFD if memfd is not supported

libvhost-user: mask F_INFLIGHT_SHMFD if memfd is not supported

libvhost-user will panic when receiving VHOST_USER_GET_INFLIGHT_FD
message if MFD_ALLOW_SEALING is not defined, since it's not able
to create a memfd.

VHOST_USER_GET_INFLIGHT_FD is used only if
VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD is negotiated. So, let's mask
that feature if the backend is not able to properly handle these
messages.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20240618100043.144657-5-sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>