The ceph_file_layout is a struct; it can get its own encode/decode/dump functions instead of us open-coding a dump function here.
In fact, I'm kind of surprised we didn't already give it one, but maybe it lies on the other side of the great MDS modernization (we didn't get all the way through last time) — we can potentially have a different one of these on every inode, so we definitely want to be able to dump it generically.