[tor-relays] "Fast" flag definition

[Igor Mitrofanov]

Hi,

It looks like 94.7% of all Running relays have the "Fast" flag now. If
that percentage becomes 100%, the flag will become meaningless.
What were the reasons behind the current definition of "Fast", and are
those still valid? If not, should "Fast" become self-adjusting
("faster than 2 Mbps or 70% of all Guard relays, whichever is
greater")?

Thanks!