Prevent players from disconnecting during the loading screen by increasing the timeout tolerance to 60 seconds for that period, fixes #5163.

The NetClient runs in the main thread, so any part of the loading screen consuming several seconds makes that client timeout.
This is a workaround because threading the NetClient would have prevent these timeouts, refs #3700.
Coutnerintuitively, since enet timeout tolerance is proportional to the latency, the better the connection of the player, the more likely it was to drop on gamestart.

This problem became very frequent in Alpha 23, at least due to the Aura bugfix rP21785, AIInterface being particularly slow and that not having been disabled yet in the loading screen resulting in additional 10 second freezes during the loading screen, even on empty maps, refs #5200, rP21838.

Differential Revision: https://code.wildfiregames.com/D1513
Based on patch by: causative