relay: Avoid false positive on network reentry detection

Bloomfilters are by design probabilistic and thus there is a small chance that we have false positive when looking them up.

When detecting network reentry, a false positive implies that the addr + port destination is then consider a reentry and the connections are refused.

Even though it is rare, that pair could be a very busy destination like wikipedia.org + 443 and so every users at that Exit would be unable to reach that destination.

Move to use an hashtable here (as a set) of addr+port so the lookup is still O(1) but with certainty. The memory footprint will be more important but still below a megabyte for all the relays to be in that set.