While the timer is designed to get started on state transition from
SIXP_TRANS_STATE_INIT, the state transition may not happen in some
erroneous situation. This change makes sure that the timer is started
once it's allocated.
- support draft-ietf-6tisch-6top-protocol-03
- maintain a sequence number per neighbor
- rename variables and constants
- reconsider file structure and file names
- make sf-simple part of example
- update sixtop/README.md
- add regression-tests for 6tisch
- apply C-DAC copyright notice
- bugfix + cleanup