In a23 it has become much more difficult to start multiplayer games, especially with large maps and many players, because players will drop during map generation. The problem occurs regardless of whether playing the new maps. This is an urgent problem since many players returned to 0ad specifically to check out a23, and we could permanently lose players since they can't get into games. In my experience it's virtually impossible to start 8 player games with random lobby players because two or three players will drop.
It is equally a problem during rejoining; players who dropped during initial map generation usually can't rejoin either.
It is caused by clients timing out when they can't perform certain aspects of map generation fast enough. elexis discovered a temporary workaround where the host can artificially increase their network lag, which causes enet to permit longer timeouts.
This patch just directly makes enet permit longer timeouts during map generation. It temporarily sets enet_peer_timeout to a high value on both client and server when map generation begins, and sets it back to a normal value once map generation has finished.
Note that elexis has a plan in the works to multithread map generation, which would also solve this problem. However, that patch is not yet ready. In the meantime, given the urgency of the situation, we need a fix.