iov_iter: Renumber ITER_* constants

Renumber the ITER_* iterator-type constants to put things in the same order
as in the iteration functions and to group user-backed iterators at the
bottom.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20230925120309.1731676-6-dhowells@redhat.com
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Jens Axboe <axboe@kernel.dk>
cc: Christoph Hellwig <hch@lst.de>
cc: Christian Brauner <christian@brauner.io>
cc: Matthew Wilcox <willy@infradead.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: David Laight <David.Laight@ACULAB.COM>
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: dhowells

include/linux/uio.h

@@ -21,12 +21,12 @@ struct kvec {
 
 enum iter_type {
 	/* iter types */
+	ITER_UBUF,
 	ITER_IOVEC,
-	ITER_KVEC,
 	ITER_BVEC,
+	ITER_KVEC,
 	ITER_XARRAY,
 	ITER_DISCARD,
-	ITER_UBUF,
 };
 
 #define ITER_SOURCE	1	// == WRITE