Changes OC-Sequence-Number back to Time and clarified
its handling & creation.

Renamed the following:
       5.3.1.  Reacting Node Endpoint Considerations  . . . . . . . . 22
       5.3.2.  Reporting Node Endpoint Considerations . . . . . . . . 23

Signed-off-by: Jouni Korhonen <jouni.korhonen@broadcom.com>