- setting the handler->state value is atomic on any POSIX implementation since
  we're dealing with an integer (enum/lxc_state_t)
- while the state clients are served it is not possible for lxc_set_state() to
  transition to the next state anyway so there's no danger in moving to the
  next state with clients missing it
- we only care about the list being modified
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>