Fix libvhost-user.c compilation.

Fix libvhost-user.c compilation.

The source file uses VIRTIO_F_VERSION_1 which is
not defined by <linux/virtio_config.h> on Debian 10.

The system-provided <linux/virtio_config.h> which
does not include the macro definition is included
through <linux/vhost.h>, so fix the issue by including
the standard-headers version before that.

Signed-off-by: David 'Digit' Turner <digit@google.com>
Message-Id: <20230405125920.2951721-2-digit@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>