Add internal inode mapping for normal multi-namespace handle mode so
large Unix inode numbers can be represented in the 28-bit inode field.
This allows OS/2 namespace clients such as Linux ncpfs to access long
names without requiring the 'o' volume option.
When ONE_DEV is active, handles encode the raw inode and cannot also
encode a namespace map index. Reuse the same device map entry across
namespaces so volumes using both 'o' and 'O' can serve OS/2 namespace
clients.
