btrfs-progs: convert: make sure the length of data chunks are also stripe aligned

Although kernel scrub code has been updated to handle the unaligned
chunk length, there is also no harm if we can allocate data chunk with
both start and length aligned.

This patch handles this by rounding up the end bytenr when allocating
data chunks for the conversion.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

convert/main.c

@@ -984,7 +984,8 @@ static int make_convert_data_block_groups(struct btrfs_trans_handle *trans,
 			u64 cur_backup = cur;
 
 			len = min(max_chunk_size,
-				  cache->start + cache->size - cur);
+				  round_up(cache->start + cache->size,
+					   BTRFS_STRIPE_LEN) - cur);
 			ret = btrfs_alloc_data_chunk(trans, fs_info, &cur_backup, len);
 			if (ret < 0)
 				break;