Performance optimisation - stage 2

The commit includes following:
- ib_path_compare_rates function optimisation.
  Insted of runtime comparison for rates, we use precomputed
  static lookup table.
- Optimisation for linked port lookup.
  Insted of two stage serach for linked port (search for link,
  search for port), now we use one one lookup. Link lookup tables
  (CAs and Switches) include index of port insted of index of
  link.
- "half world" CPU time is printed into log (as INFO)