Adjust the rules for warning about too many connections.

Previously we tolerated up to 1.5 connections for every relay we were connected to, and didn't warn if we had fewer than 5 connections total.

Now we tolerate up to 1.5 connections per relay, and up to 4 connections per authority, and we don't warn at all when we have fewer than 25 connections total.

Fixes bug 33880, which seems to have been provoked by our #17592 (closed) change in 0.3.5.