svc/connect.in: Maintain time of last reconnect attempt and add rate limit.
This isn't used yet, but it's there as a general mechanism.
Don't rate-limit reconnections provoked by the pinger internally because
(a) these are relatively infrequent anyway by the nature of the pinger
mechanism, and (b) the current rate-limiting strategy is simply to
ignore a reconnection request if we've already made an attempt fairly
recently, so there isn't (and it's not worth building) the necessary
machinery to defer reconnection, and determine whether a deferred
reconnection is still needed.
~mdw / tripe / commit