locitest: run all messages through the validator

The only failures are OF 1.2+ flow mods due to the variable-offset instructions
member.
loci: correctly validate instructions member in flow mods

The instructions list comes after the variable-length match structure.
flow stats setup: support OF 1.1+ effects

Not sure why I had to move the code block. Doing the instructions set before
the match magic resulted in an empty instructions list.
loci: fix OXM class and lengths

The class is now hardcoded to 0x8000 (OpenFlow Basic) instead of 0 (NXM).

The length of an OXM element does not include the header.
loci: allow dumping OF 1.3 objects
loci: fix version used to initialize wire match objects

We need to use the same version as the destination message, not the source
match.
type_maps: fix type value for of_match_v3
loci: fix packet out action len for OF 1.1+

OF 1.1+ packet-out messages have 6 bytes of padding in the fixed length part of
the object after actions_len.
loci: fix of_wire_buffer_replace_data for non-trailing members

The previous code only worked correctly if the member being grown was the last
non-zero-length member in the object.
loci: fix OF 1.2+ packet-in data offset

There are two bytes of padding between the match and the packet data.

This commit introduces "extra length", which is the sum of the fixed length
parts of an object having variable offsets (after a variable length member).
The only use is for OF 1.2+ packet-in messages.
Merge into master from pull request #33:
Fix OF 1.3 flow mods, flow stats, and OXM (https://github.com/floodlight/loxigen/pull/33)