endian-ness tags

Hi!
I've been thinking about the endian-ness tags for legacy devices.
We currentl have a note on legacy endian-ness
before each structure.
This violates the clean separation of legacy
in separate sections.
It's not too bad but I'd like to find a way to improve this
before 1.0.

For legacy it's mostly consistent:
device specific stuff and in-memory stuff is native endian

Exceptions:
PCI common virtio header is little endian
but it is not documented using a struct.
(balloon is only exception).

CCW already uses BEXX

MMIO isn't using C structs at all.

Proposal:

- say "LEXX means: Little Endian for 1.0 interfaces and Guest Endian for Legacy interfaces".
- change balloon config from C struct to a table specifying endian-ness
  explicitly instead of LEXX.

I created https://tools.oasis-open.org/issues/browse/VIRTIO-58
to track this.

-- 
MST