OFConnectionManager: implement bsn_log extension

This allows the controller to ask us to output a log message, subject to our
configured loglevel. It's useful for log correlation.
update loxigen-artifacts

* submodules/loxigen-artifacts c4933b5...541b6c3 (7):
  > Artifacts from https://github.com/floodlight/loxigen/compare/7d9242512ccec48103ac0358ebe69cac7ff49a31...3805ffaa4eb58eb134017219dbbe12537aa20caf
  > Artifacts from https://github.com/floodlight/loxigen/compare/eeaa0005c4ee22087bffacc60b7dff420d3fc2cc...7d9242512ccec48103ac0358ebe69cac7ff49a31
  > Artifacts from https://github.com/floodlight/loxigen/compare/cc956a90f13c4088df6fd9f8921f3583ef9e931f...eeaa0005c4ee22087bffacc60b7dff420d3fc2cc
  > Artifacts from https://github.com/floodlight/loxigen/compare/d421394c0f231ec63a4863ecec5abfccf16a6a7b...cc956a90f13c4088df6fd9f8921f3583ef9e931f
  > Artifacts from https://github.com/floodlight/loxigen/compare/dd9c2f3b010914f40ec42e7ee3c39dd454f1c73a...d421394c0f231ec63a4863ecec5abfccf16a6a7b
  > Artifacts from https://github.com/floodlight/loxigen/compare/4648c6f6bc38ba2d0d44b6446d8dc825b2e1dae0...dd9c2f3b010914f40ec42e7ee3c39dd454f1c73a
  > Artifacts from https://github.com/floodlight/loxigen/compare/c8f68f067a7e49da5a1dd512456a089d626c3c27...4648c6f6bc38ba2d0d44b6446d8dc825b2e1dae0
Merge into master from pull request #151:
OFConnectionManager: implement bsn_log extension (https://github.com/floodlight/indigo/pull/151)