This commit moves the call to conf_activate_modules() out of the
set_config() function and into main() so that global query modules are
activated after privilege dropping has occurred.

This makes the global query modules match the zone query modules a
little better. The zone query modules are activated later, after
privilege dropping has occurred.

This ensures that if a global query module launches its own threads at
startup, those threads are spawned from a main thread that has already
performed privilege dropping.