vhost-user: fix log size

commit 2b8819c6
("vhost-user: modify SET_LOG_BASE to pass mmap size and offset")
passes log size in units of 4 byte chunks instead of the
expected size in bytes.

Fix this up.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/vhost-user.c

@@ -206,7 +206,7 @@ static int vhost_user_set_log_base(struct vhost_dev *dev, uint64_t base,
     VhostUserMsg msg = {
         .request = VHOST_USER_SET_LOG_BASE,
         .flags = VHOST_USER_VERSION,
-        .payload.log.mmap_size = log->size,
+        .payload.log.mmap_size = log->size * sizeof(*(log->log)),
         .payload.log.mmap_offset = 0,
         .size = sizeof(msg.payload.log),
     };