Make it even harder to become HSDir

In legacy/trac#8243 (moved) we started requiring Stable flag for becoming HSDirs, but this is still not hard enough for motivated adversaries. Hence we need to make it even harder for a relay to become HSDir, so that only relays that have been around for long get the flag. After prop224 gets deployed, there will be less incentive for adversaries to become HSDirs since they won't be able to harvest onion addresses.

Until then, our current plan is to increase the bandwidth and uptime required to become an HSDir to something almost unreasonable. For example requiring an uptime of over 6 months, or maybe requiring that the relay is in the top 1/4th of uptimes on the network.