vhost-scsi: Enable VIRTIO_RING_F_EVENT_IDX

It was disabled as a workaround. Now userspace bits work fine with it.
The broken version was not ever committed to QEMU, I guess the same is
true for nlkt.

So, let's enable it.

Signed-off-by: Asias He <asias@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/scsi.c

@@ -162,14 +162,8 @@ enum {
 	VHOST_SCSI_VQ_IO = 2,
 };
 
-/*
- * VIRTIO_RING_F_EVENT_IDX seems broken. Not sure the bug is in
- * kernel but disabling it helps.
- * TODO: debug and remove the workaround.
- */
 enum {
-	VHOST_SCSI_FEATURES = (VHOST_FEATURES & (~VIRTIO_RING_F_EVENT_IDX)) |
-			      (1ULL << VIRTIO_SCSI_F_HOTPLUG)
+	VHOST_SCSI_FEATURES = VHOST_FEATURES | (1ULL << VIRTIO_SCSI_F_HOTPLUG)
 };
 
 #define VHOST_SCSI_MAX_TARGET	256