OFConnectionManager: transition to HANDSHAKE_COMPLETE after features reply is enqueued

Reviewer: @kenchiang

Without this change, any code that executes on the state transition (such as 
ind_cxn_status_notify, indigo_core_connection_count_notify, and the connection 
status callbacks) will see an inconsistent state. The connection would already 
be in state HANDSHAKE_COMPLETE, but the features reply wouldn't have been sent 
to the controller. Any message sent to the controller due to the state change 
would arrive before the features reply.

We saw this specifically with the async bsn_controller_connections message.