loci: replace validator with a stub

The negative unit tests are commented out since the stub validator doesn't do
anything.
loci: generate validator class hierachies

Includes object length checks. Does not validate lists yet.
loci: validate fixed-offset non-field-length lists

This is enough to pass all the existing unit tests.
loci: read and validate field-length members
loci: validate lists that use field-length members
loci: add TODOs to validator
Fix C backend for bsn_vport.
Merge remote-tracking branch 'upstream/master'
Merge into master from pull request #252:
Fix bsn_vport subtype and add l2gre vport (https://github.com/floodlight/loxigen/pull/252)
Merge into master from pull request #251:
BSN Image Desc Stats Req, Reply (https://github.com/floodlight/loxigen/pull/251)
add util function for multiple pkt in reasons
add java doc
Merge into master from pull request #254:
add util function for multiple pkt in reasons (https://github.com/floodlight/loxigen/pull/254)
of_tunnel_id support for OXM is added.
toString methods are overrided for ICMPv4Code and ICMPv4Type
javadoc updated.
loci: remove unused validator import
Merge into master from pull request #245:
Rewrite LOCI validator (https://github.com/floodlight/loxigen/pull/245)
loci: fix compiler warning due to large constant
Merge into master from pull request #256:
loci: fix compiler warning due to large constant (https://github.com/floodlight/loxigen/pull/256)