bcachefs: bcachefs_metadata_version_disk_accounting_big_endian

bcachefs: bcachefs_metadata_version_disk_accounting_big_endian

Fix sort order for disk accounting keys, in order to fix a regression on
mount times.

The typetag is now the most significant byte of the key, meaning disk
accounting keys of the same type now sort together.

This lets us skip over disk accounting keys that aren't mirrored in
memory when reading accounting at startup, instead of having them
interleaved with other counter types.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>