[link] improve datalink/telemetry report

- more reported data about up/down-link
- cleanup report messages
- display link page in GCS even in single link mode

Tested in simulation, will be on real hardware soon.
Test with redundant link would be welcome since I don't have working setup for this.
This should be a float...
Or use get_sys_time_usec() which has higher resolution (get_sys_time_float() has only sys_time.resolution)...