openflow_input: add bsn_role_status extension

This is a backport of the OpenFlow 1.4 message.
openflow_input: add bsn_connections extension
openflow_input: rename bsn_connections to bsn_controller_connections

Also added some comments.
Merge into master from pull request #159:
Role status and connection list messages (https://github.com/floodlight/loxigen/pull/159)