In a large pot over medium heat, add the olive oil, garlic, ginger and lemongrass. Give it a stir, then add the curry, crushed red pepper flakes and the broth. Increase the heat to medium-high bringing the broth to a light boil. Add the shrimp and reduce the heat to medium. Simmer for 3 minutes. Add the coconut milk and cabbage. Increase the heat just a bit and as soon as the soup comes to another very light simmer, remove it from the heat.