Revert "MP Lobby: reduced frequency of network polls (100ms -> 1000ms)"

This reverts commit 5fd833a. It was causing the lobby to
lag up to *three minutes* behind current activity due to multiple data packets being queued
(see #3046). It seems 100 ms was enough to mask this issue.

src/game_config.cpp

@@ -83,7 +83,7 @@ double hex_brightening = 1.25;
 //
 int cache_compression_level = 6;
 
-unsigned lobby_network_timer  = 1000;
+unsigned lobby_network_timer  = 100;
 unsigned lobby_refresh        = 4000;
 
 const std::string observer_team_name = "observer";