cilium: docs update encryption algo example to use GCM
cilium: docs update encryption algo example to use GCM

Use modern GCM-128-AES algorithm in encryption example. We see
better performance with this algorithm.

Signed-off-by: John Fastabend <ee461b60978bea1c76b3018c0b89685175b248e2@gmail.com>

cilium/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,cilium-team/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,cilium-team/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium