Only include valid peer locations in link length probe response.
Make link length probe response less identifying.

By sorting the reported link lengths, we maintain the statistical usefulness
of the data, but do no longer provide information on the particular order of
our peers (which should not be relevant for analysis anyhow).
Don't use allowCrazy: upstream doesn't have it anymore. Assume our location is valid here.
Merge branch 'probe-link-lengths' of github.com:bertm/fred-staging into next