MINOR: connection: update rhttp flags usage

MINOR: connection: update rhttp flags usage

Change the flags used for reversed connection :
* CO_FL_REVERSED is now put after reversal for passive connect. For
  active connect, it is delayed when accept is completed after reversal.
* CO_FL_ACT_REVERSING replace the old CO_FL_REVERSED. It is put only for
  active connect on reversal and removes once accept is done.

This allows to identify a connection as reversed during its whole
lifetime. This should be useful to extend reverse connect.