pipe: allow passing around of ops private pointer

relay needs this for proper consumption handling, and the network
receive support needs it as well to lookup the sk_buff on pipe
release.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/splice.c b/fs/splice.c
index bea9f15..00850e5 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -185,6 +185,7 @@
 			buf->page = spd->pages[page_nr];
 			buf->offset = spd->partial[page_nr].offset;
 			buf->len = spd->partial[page_nr].len;
+			buf->private = spd->partial[page_nr].private;
 			buf->ops = spd->ops;
 			if (spd->flags & SPLICE_F_GIFT)
 				buf->flags |= PIPE_BUF_FLAG_GIFT;