Tighten the server+client timeouts

Now that there is a working heartbeat mechanism between the
server<->client, 5 seconds timeout on the server without hearing from
the client is excessive, even 3 seconds is extremely generous on a LAN.

On the client side, 2 seconds without receiving a response from the
server on a LAN connection definitely means the server is gone, and the
reconnection system will be triggered as usual