update loci to b8957d6b02d68b19fa531bdfe89783a13d2d4f7f

 * Adds bsn_disable_src_mac_check extension instruction
Merge into master from pull request #69:
update loci to b8957d6b02d68b19fa531bdfe89783a13d2d4f7f (https://github.com/floodlight/indigo/pull/69)