Btrfs: mark delayed refs as for cow

Add a for_cow parameter to add_delayed_*_ref and pass the appropriate value
from every call site. The for_cow parameter will later on be used to
determine if a ref will change anything with respect to qgroups.

Delayed refs coming from relocation are always counted as for_cow, as they
don't change subvol quota.

Also pass in the fs_info for later use.

btrfs_find_all_roots() will use this as an optimization, as changes that are
for_cow will not change anything with respect to which root points to a
certain leaf. Thus, we don't need to add the current sequence number to
those delayed refs.

Signed-off-by: Arne Jansen <sensille@gmx.net>
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

fs/btrfs/inode.c

@@ -3139,7 +3139,7 @@ delete:
 			ret = btrfs_free_extent(trans, root, extent_start,
 						extent_num_bytes, 0,
 						btrfs_header_owner(leaf),
-						ino, extent_offset);
+						ino, extent_offset, 0);
 			BUG_ON(ret);
 		}