Why Drupal changes the module (system table) bootstrap value after i set it with an SQL query?
ok got it,

in system.module there is a function called _system_update_bootstrap_status()

this function changes bootstrap value to '1' for all modules that implement one (or more) of the hooks: 'boot', 'exit', 'watchdog', 'language_init'

so i just needed to implement an empty hook_boot() and my module is present in bootstrap.