do not include experimenter OXMs in of_oxm_type_to_id

This table is keyed by OXM type, not including the class. OXMs in different
classes will collide.
add of_oxm_bsn_lag_id
java_gen: support bsn_lag_id OXM
add testcases for of_oxm_bsn_lag_id
java_gen: use LagId type for the bsn_lag_id OXM
Merge into master from pull request #105:
add of_oxm_bsn_lag_id (https://github.com/floodlight/loxigen/pull/105)