openflow_input: add bsn_disable_src_mac_check extension instruction
add bsn_disable_src_mac_check testcase
java_gen: support extension instructions
java_gen: support testing classes without builders

Some classes, like OFInstructionBsnDisableSrcMacCheck, don't have any data
members and so have a single immutable instance and no builder. This change
fixes the unit tests to use the correct factory method.
pyloxi: support of_instruction_bsn_disable_src_mac_check
loci: support of_instruction_bsn_disable_src_mac_check
pyloxi: fix special parsing case for experimenter instructions
Merge into master from pull request #139:
add bsn_disable_src_mac_check instruction (https://github.com/floodlight/loxigen/pull/139)