Combine 2 teaspoons dill, 2 teaspoons chives, 1 teaspoon garlic powder, the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper in a small bowl. Place cornflakes in a shallow dish. Remove the chicken from the buttermilk and shake off the excess. Sprinkle the herb mixture all over the drumsticks, then roll them in the cornflakes, coating well. Transfer to the prepared baking sheet and coat all sides with cooking spray.