[tor-relays] CPU saturation attack/abuse

[Dhalgren Tor]

Found other ones:  December 24 where egress was much higher then
ingress (but crypto-workers were pegged, not main thread).  December
28 & 29, attack like today.  Feburary 1 & 2, like today with ingress
higher than egress.

In today's and the latter-two above the main event thread was pegged
either continuously or intermittently with ingress higher than egress.

Just looked again and see all threads, crypto-worker and main-event
pegging episodically.