bpf, xdp: migrate prefilter program to generic __ctx_buff
bpf, xdp: migrate prefilter program to generic __ctx_buff

As the subject says, convert prefilter over to generic __ctx_buff.

Signed-off-by: Daniel Borkmann <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@iogearbox.net>

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