Btrfs: Avoid orphan inodes cleanup while replaying log

We do log replay in a single transaction, so it's not good to do unbound
operations. This patch cleans up orphan inodes cleanup after replaying
the log. It also avoids doing other unbound operations such as truncating
a file during replaying log. These unbound operations are postponed to
the orphan inode cleanup stage.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>