Add missing MP settings for reloaded games. Fixes #21808.

The problam was that mp::configure is not used for reloaded games and so
mp_game_settings will not be fully initialised. This leads to using default
values rather than values set using mp::configure screen or from reloaded game
config.

The optimal solution would be to either display mp::configure for reloaded games
or to populate mp_game_settings using reloaded game config. However, both
solutions require rather a lot of code restructing and are probably not suitable
for a feature freeze.