net: Convert to new qapi union layout

net: Convert to new qapi union layout

We have two issues with our qapi union layout:
1) Even though the QMP wire format spells the tag 'type', the
C code spells it 'kind', requiring some hacks in the generator.
2) The C struct uses an anonymous union, which places all tag
values in the same namespace as all non-variant members. This
leads to spurious collisions if a tag value matches a non-variant
member's name.

Make the conversion to the new layout for net-related code.

Signed-off-by: Eric Blake <[email protected]>
Message-Id: <1445898903[email protected]>
[Commit message tweaked slightly]
Signed-off-by: Markus Armbruster <[email protected]>