pafd reports misleading idle time for v2 clients

[m-ronnblom]

The Pathfinder server's "clients" Pathfinder protocol command reports v2 clients as being active (non-idle) only every 15 s (with default settings), even though no Pathfinder protocol level messages were seen from the client.

A v2 client is considered alive as long as its protocol level connection is up, however the "idle" field in the "clients" notification messages may (and maybe should) be something else than known-to-be-alive.

The server should either treat a v2 client as always active (as long as the transport connection is up), or only active when it's sending protocol level messages.